Hygiene hypothesis
Encyclopedia
In medicine
, the Hygiene Hypothesis
states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms (e.g., gut flora
or probiotics), and parasites increases susceptibility to allergic
diseases by suppressing natural development of the immune system
. The rise of autoimmune diseases and acute lymphoblastic leukemia
in young people in the developed world has also been linked to the hygiene hypothesis. There is some evidence that autism
may be caused by an immune disease; One study supports the hygiene hypothesis theory and cites the lack of early childhood exposure as a cause of autism.
(now the BMJ), in 1989. In this article, the hygiene hypothesis was proposed to explain the observation that hay fever
and eczema
, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child.
The hygiene hypothesis has been extensively investigated by immunologists
and epidemiologists
and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that has been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.
-mediated immune response. Many bacteria
and viruses elicit a Th1
-mediated immune response, which down-regulates Th2 responses. The first proposed mechanism of action of the hygiene hypothesis stated that insufficient stimulation of the Th1 arm, stimulating the cell defence of the immune system, leads to an overactive Th2 arm, stimulating the antibody-mediated immunity of the immune systems, which in turn led to allergic disease.
The first proposed mechanistic explanation for the hygiene hypothesis cannot explain the rise in incidence (similar to the rise of allergic diseases) of several Th1-mediated autoimmune diseases
, including inflammatory bowel disease
(IBD), multiple sclerosis
(MS), and type I diabetes
. The major proposed alternative mechanistic explanation is that the developing immune system must receive stimuli (from infectious agents, symbiotic bacteria, or parasites) in order to adequately develop regulatory T cells, or it will be more susceptible to autoimmune diseases and allergic diseases, because of insufficiently repressed Th1 and Th2 responses, respectively.
, various mycobacteria
, and certain helminths
.
Studies in mice have shown that exposure of young mice to viruses can result in a decreased incidence of diabetes.
In Cell : http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WSN-4C56FTV-F-F&_cdi=7051&_user=10&_coverDate=04%2F16%2F2004&_sk=%23TOC%237051%232004%23998829997%23496480%23FLA%23display%23Volume_117,_Issue_2,_Pages_145-277_(16_April_2004)%23tagged%23Volume%23first%3D117%23Issue%23first%3D2%23Pages%23first%3D145%23last%3D277%23date%23(16_April_2004)%23&view=c&_gw=y&wchp=dGLbVtb-zSkWA&_valck=1&md5=db4d7ee7fa5574bbe87414ac0e9e34d4&ie=/sdarticle.pdfHomeostatic Expansion of T Cells during Immune Insufficiency Generates Autoimmunity] they showed that when short lived T cells were replaced during a state of too few long lived T-cells (Memory T cell), because of lack of infections, the risk of developing autoimmune diseases will increase. They showed that in a state of too few long lived T-cells, because of lack of infections, not enough short lived T-cells could be produced by long lived T-cells during homeostatic expansion. Therefore, more auto reactive T-cells will divide in such a state, causing multiplying auto reactive T-cells with a greater risk of causing autoimmune diseases like type I diabetes or MS
.
One conclusion is that a clean environment, with lack of infections (like early life infections) increases the risk of an autoimmune disorder.
Th2 immune disorders such as asthma
and other allergic diseases
are probably related to the hygiene hypothesis. A baby has many Th2 cells, which stimulate the production of antibodies. When not sufficiently stimulated with early life diseases, the immune system will have too many Th2 cells present, leading to a greater risk of Th2 immune disorder. If a child is exposed to infection diseases then the cell defense will be stimulated via Th1 cells causing a reduction of Th2 cells and subsequently a reduction of antibody stimulation by Th2 and therefore a lower risk of developing an allergic disease such as asthma
. Unfortunately, vaccination only uses the Th2 mechanism.
In developed countries where childhood diseases were eliminated, the asthma rate for youth is approximately 10%. In the 19th century, asthma was a very rare disease.
Longitudinal studies in the third world demonstrate an increase in immunological disorders as a country grows more affluent and, presumably, cleaner. The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. The use of antibacterial cleaning products has also been associated with higher incidence of asthma
, as has birth by Caesarean section rather than vaginal birth. However, the studies investigating these links showed only tenuous correlations between the factors described and the conditions they are hypothesized to cause.
Several pieces of experimental evidence also support the hygiene hypothesis. Work performed in the laboratory of Professor Anne Cooke at the University of Cambridge
showed that mice of the NOD
strain (which spontaneously develop type 1 diabetes mellitus
) had a significantly reduced incidence of this disease when infected with the helminth parasite Schistosoma mansoni
.
In November 2009 a group of researchers at the School of Medicine at University of California, San Diego, found that Staphylococci helped reduce inflammation.
A double blind study performed on 2500 pregnant women in Uganda showed that infants of the women treated with anthelminthic medication for worm infections had double the rate of doctor-diagnosed infantile eczema.
Because of the promise shown by this research, two versions of Helminthic therapy
, using Trichuris suis
ova or Necator americanus
larvae, have become available.
Helminthic therapy is the treatment of autoimmune disease
s and immune disorder
s by means of deliberate infestation with a helminth or with the ova of a helminth. Helminthic therapy is currently being studied as a promising treatment for several (non-viral) autoimmune disease
s including Crohn's disease
, multiple sclerosis
, asthma
, and ulcerative colitis
. Autoimmune liver disease has also been demonstrated to be modulated by active helminth infections.
In addition to the treatment of immune disorders the anti-inflammatory effects of helminth infection are prompting interest and research into diseases that involve inflammation but that are not currently considered to include autoimmunity or immune dysregulation as a causative factor. Heart disease and arteriosclerosis both have similar epidemiological profiles as autoimmune diseases and both involve inflammation. Nor can their increase be solely attributed to environmental factors. Recent research has focused on the eradication of helminths to explain this discrepancy.
As a result of the hygiene hypothesis helminthic therapy emerged from the extensive research into why the incidence of immunological disorders and autoimmune diseases is relatively low in less developed countries, while there has been a significant and sustained increase in immunological disorders and autoimmune diseases in the industrialized countries. If helminthic therapy and other therapies using other types of infectious organisms, such as protozoa, to treat disease are proven successful and safe the hygiene hypothesis has potentially large implications for the practice of medicine in the future.
in developed nations, many of which are also related to the other. A few other major areas of focus in the literature include infant feeding, over-exposure to certain allergens and exposure to certain pollutants. Infant feeding covers a range of topics which include whether babies are breast fed or not and for how long, when they are introduced to solid foods and the type of these foods, whether they are given cow's milk and even the types of processing that the milk undergoes. Numerous articles have reported that over-exposure to certain allergens in occupational situations can cause allergic diseases, such as Laboratory animal allergy
, bird lung
, farmer's lung
, and bakers lung (See Wheat allergy
). The third of these theories suggests that pollution (such as diesel exhaust) might be responsible for the increase of these diseases; however, some also claim that developed nations have also been becoming cleaner, and much more so than in the bleak Dickensian years of the early industrial revolution
.
For immunological conditions related to Strachan's original version of the hygiene hypothesis, such as atopy
and asthma
, the pool chlorine hypothesis
was proposed by Albert Bernard and his colleagues as an alternative hypothesis based on epidemiological
evidence in 2003.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, the Hygiene Hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms (e.g., gut flora
Gut flora
Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora....
or probiotics), and parasites increases susceptibility to allergic
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
diseases by suppressing natural development of the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
. The rise of autoimmune diseases and acute lymphoblastic leukemia
Acute lymphoblastic leukemia
Acute lymphoblastic leukemia is a form of leukemia, or cancer of the white blood cells characterized by excess lymphoblasts.Malignant, immature white blood cells continuously multiply and are overproduced in the bone marrow. ALL causes damage and death by crowding out normal cells in the bone...
in young people in the developed world has also been linked to the hygiene hypothesis. There is some evidence that autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
may be caused by an immune disease; One study supports the hygiene hypothesis theory and cites the lack of early childhood exposure as a cause of autism.
History
Although the idea that exposure to certain infections may decrease the risk of an allergy is not new, David P. Strachan was the first scientist who gave the theory a scientific background in an article published in the British Medical JournalBritish Medical Journal
BMJ is a partially open-access peer-reviewed medical journal. Originally called the British Medical Journal, the title was officially shortened to BMJ in 1988. The journal is published by the BMJ Group, a wholly owned subsidiary of the British Medical Association...
(now the BMJ), in 1989. In this article, the hygiene hypothesis was proposed to explain the observation that hay fever
Hay Fever
Hay Fever is a comic play written by Noël Coward in 1924 and first produced in 1925 with Marie Tempest as the first Judith Bliss. Laura Hope Crews played the role in New York...
and eczema
Eczema
Eczema is a form of dermatitis, or inflammation of the epidermis . In England, an estimated 5.7 million or about one in every nine people have been diagnosed with the disease by a clinician at some point in their lives.The term eczema is broadly applied to a range of persistent skin conditions...
, both allergic diseases, were less common in children from larger families, which were presumably exposed to more infectious agents through their siblings, than in children from families with only one child.
The hygiene hypothesis has been extensively investigated by immunologists
Immunology
Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders ; the...
and epidemiologists
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
and has become an important theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that has been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as important modulators of immune system development, along with infectious agents.
Mechanism of action
Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a Th2T helper cell
T helper cells are a sub-group of lymphocytes, a type of white blood cell, that play an important role in the immune system, particularly in the adaptive immune system. These cells have no cytotoxic or phagocytic activity; they cannot kill infected host cells or pathogens. Rather, they help other...
-mediated immune response. Many bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and viruses elicit a Th1
T helper cell
T helper cells are a sub-group of lymphocytes, a type of white blood cell, that play an important role in the immune system, particularly in the adaptive immune system. These cells have no cytotoxic or phagocytic activity; they cannot kill infected host cells or pathogens. Rather, they help other...
-mediated immune response, which down-regulates Th2 responses. The first proposed mechanism of action of the hygiene hypothesis stated that insufficient stimulation of the Th1 arm, stimulating the cell defence of the immune system, leads to an overactive Th2 arm, stimulating the antibody-mediated immunity of the immune systems, which in turn led to allergic disease.
The first proposed mechanistic explanation for the hygiene hypothesis cannot explain the rise in incidence (similar to the rise of allergic diseases) of several Th1-mediated autoimmune diseases
Autoimmunity
Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease...
, including inflammatory bowel disease
Inflammatory bowel disease
In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis.-Classification:...
(IBD), multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
(MS), and type I diabetes
Diabetes mellitus type 1
Diabetes mellitus type 1 is a form of diabetes mellitus that results from autoimmune destruction of insulin-producing beta cells of the pancreas. The subsequent lack of insulin leads to increased blood and urine glucose...
. The major proposed alternative mechanistic explanation is that the developing immune system must receive stimuli (from infectious agents, symbiotic bacteria, or parasites) in order to adequately develop regulatory T cells, or it will be more susceptible to autoimmune diseases and allergic diseases, because of insufficiently repressed Th1 and Th2 responses, respectively.
Breadth of the hypothesis
The hygiene hypothesis has expanded from eczema and hay fever to include exposure to several varieties of microorganisms and parasites, with which humans coexisted throughout much of our evolutionary history, as necessary for balanced and regulated immune system development. In recent times, the development of hygienic practices, elimination of childhood diseases, widespread use of antibiotics, and relative availability of effective medical care have diminished or eliminated exposure to these microorganisms and parasites during development. Examples of organisms that may be important for proper development of T regulatory cells include lactobacilliLactobacillus
Lactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic rod-shaped bacteria. They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. They are common and usually benign...
, various mycobacteria
Mycobacterium
Mycobacterium is a genus of Actinobacteria, given its own family, the Mycobacteriaceae. The genus includes pathogens known to cause serious diseases in mammals, including tuberculosis and leprosy...
, and certain helminths
Parasitic worm
Parasitic worms or helminths are a division of eukaryoticparasites that, unlike external parasites such as lice and fleas, live inside their host. They are worm-like organisms that live and feed off living hosts, receiving nourishment and protection while disrupting their hosts' nutrient...
.
Supporting evidence
The hygiene hypothesis is supported by epidemiological data. Studies have shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world.Studies in mice have shown that exposure of young mice to viruses can result in a decreased incidence of diabetes.
In Cell : http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WSN-4C56FTV-F-F&_cdi=7051&_user=10&_coverDate=04%2F16%2F2004&_sk=%23TOC%237051%232004%23998829997%23496480%23FLA%23display%23Volume_117,_Issue_2,_Pages_145-277_(16_April_2004)%23tagged%23Volume%23first%3D117%23Issue%23first%3D2%23Pages%23first%3D145%23last%3D277%23date%23(16_April_2004)%23&view=c&_gw=y&wchp=dGLbVtb-zSkWA&_valck=1&md5=db4d7ee7fa5574bbe87414ac0e9e34d4&ie=/sdarticle.pdfHomeostatic Expansion of T Cells during Immune Insufficiency Generates Autoimmunity] they showed that when short lived T cells were replaced during a state of too few long lived T-cells (Memory T cell), because of lack of infections, the risk of developing autoimmune diseases will increase. They showed that in a state of too few long lived T-cells, because of lack of infections, not enough short lived T-cells could be produced by long lived T-cells during homeostatic expansion. Therefore, more auto reactive T-cells will divide in such a state, causing multiplying auto reactive T-cells with a greater risk of causing autoimmune diseases like type I diabetes or MS
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
.
One conclusion is that a clean environment, with lack of infections (like early life infections) increases the risk of an autoimmune disorder.
Th2 immune disorders such as asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
and other allergic diseases
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
are probably related to the hygiene hypothesis. A baby has many Th2 cells, which stimulate the production of antibodies. When not sufficiently stimulated with early life diseases, the immune system will have too many Th2 cells present, leading to a greater risk of Th2 immune disorder. If a child is exposed to infection diseases then the cell defense will be stimulated via Th1 cells causing a reduction of Th2 cells and subsequently a reduction of antibody stimulation by Th2 and therefore a lower risk of developing an allergic disease such as asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
. Unfortunately, vaccination only uses the Th2 mechanism.
In developed countries where childhood diseases were eliminated, the asthma rate for youth is approximately 10%. In the 19th century, asthma was a very rare disease.
Longitudinal studies in the third world demonstrate an increase in immunological disorders as a country grows more affluent and, presumably, cleaner. The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. The use of antibacterial cleaning products has also been associated with higher incidence of asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, as has birth by Caesarean section rather than vaginal birth. However, the studies investigating these links showed only tenuous correlations between the factors described and the conditions they are hypothesized to cause.
Several pieces of experimental evidence also support the hygiene hypothesis. Work performed in the laboratory of Professor Anne Cooke at the University of Cambridge
University of Cambridge
The University of Cambridge is a public research university located in Cambridge, United Kingdom. It is the second-oldest university in both the United Kingdom and the English-speaking world , and the seventh-oldest globally...
showed that mice of the NOD
NOD mice
Non-obese diabetic or NOD mice, like the Biobreeding rat, are used as an animal model for type 1 diabetes.- History :Non-obese diabetic mice exhibit a susceptibility to spontaneous development of autoimmune insulin dependent diabetes mellitus...
strain (which spontaneously develop type 1 diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
) had a significantly reduced incidence of this disease when infected with the helminth parasite Schistosoma mansoni
Schistosoma mansoni
Schistosoma mansoni is a significant parasite of humans, a trematode that is one of the major agents of the disease schistosomiasis. The schistosomiasis caused by Schistosoma mansoni is intestinal schistosomiasis....
.
In November 2009 a group of researchers at the School of Medicine at University of California, San Diego, found that Staphylococci helped reduce inflammation.
A double blind study performed on 2500 pregnant women in Uganda showed that infants of the women treated with anthelminthic medication for worm infections had double the rate of doctor-diagnosed infantile eczema.
Helminthic therapy
The use of parasitic worms (also known as helminths) to treat the types of disease described by the hygiene hypothesis is being studied in the UK, USA and Australia.Because of the promise shown by this research, two versions of Helminthic therapy
Helminthic therapy
Helminthic therapy, a type of immunotherapy, is the treatment of autoimmune diseases and immune disorders by means of deliberate infestation with a helminth or with the ova of a helminth. Helminths are parasitic worms such as hookworms and whipworms....
, using Trichuris suis
Trichuris suis
Trichuris suis is a whipworm; the variations in thickness of the anterior and posterior segments give the parasite the characteristic “whip-like” appearance. Adult females measure 6 to 8 cm and adult males 3 to 4 cm. T. suis eggs are oval and yellow-brown with bipolar plugs.T...
ova or Necator americanus
Necator americanus
Necator americanus is a species of Necator. It is a class within the phylum Nematodes and commonly known as New World hookworm. It is a parasitic nematode worm that lives in the small intestine of hosts such as humans, dogs and cats. It is responsible for Necatoriasis...
larvae, have become available.
Helminthic therapy is the treatment of autoimmune disease
Autoimmune disease
Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. In other words, the body actually attacks its own cells. The immune system mistakes some part of the body as a pathogen and attacks it. This may be restricted to...
s and immune disorder
Immune disorder
An immune disorder is a dysfunction of the immune system. These disorders can be characterized in several different ways:* By the component of the immune system affected* By whether the immune system is overactive or underactive...
s by means of deliberate infestation with a helminth or with the ova of a helminth. Helminthic therapy is currently being studied as a promising treatment for several (non-viral) autoimmune disease
Autoimmune disease
Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. In other words, the body actually attacks its own cells. The immune system mistakes some part of the body as a pathogen and attacks it. This may be restricted to...
s including Crohn's disease
Crohn's disease
Crohn's disease, also known as regional enteritis, is a type of inflammatory bowel disease that may affect any part of the gastrointestinal tract from mouth to anus, causing a wide variety of symptoms...
, multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
, asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, and ulcerative colitis
Ulcerative colitis
Ulcerative colitis is a form of inflammatory bowel disease . Ulcerative colitis is a form of colitis, a disease of the colon , that includes characteristic ulcers, or open sores. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset...
. Autoimmune liver disease has also been demonstrated to be modulated by active helminth infections.
In addition to the treatment of immune disorders the anti-inflammatory effects of helminth infection are prompting interest and research into diseases that involve inflammation but that are not currently considered to include autoimmunity or immune dysregulation as a causative factor. Heart disease and arteriosclerosis both have similar epidemiological profiles as autoimmune diseases and both involve inflammation. Nor can their increase be solely attributed to environmental factors. Recent research has focused on the eradication of helminths to explain this discrepancy.
As a result of the hygiene hypothesis helminthic therapy emerged from the extensive research into why the incidence of immunological disorders and autoimmune diseases is relatively low in less developed countries, while there has been a significant and sustained increase in immunological disorders and autoimmune diseases in the industrialized countries. If helminthic therapy and other therapies using other types of infectious organisms, such as protozoa, to treat disease are proven successful and safe the hygiene hypothesis has potentially large implications for the practice of medicine in the future.
Alternative hypotheses
There are many other hypotheses which aim to explain the increase in allergiesAllergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
in developed nations, many of which are also related to the other. A few other major areas of focus in the literature include infant feeding, over-exposure to certain allergens and exposure to certain pollutants. Infant feeding covers a range of topics which include whether babies are breast fed or not and for how long, when they are introduced to solid foods and the type of these foods, whether they are given cow's milk and even the types of processing that the milk undergoes. Numerous articles have reported that over-exposure to certain allergens in occupational situations can cause allergic diseases, such as Laboratory animal allergy
Laboratory animal allergy
Laboratory animal allergy is an occupational disease of laboratory animal technicians and scientists. It manifests as an allergic response to animal urine, specifically the major urinary proteins of rodents, and can lead to the development of asthma...
, bird lung
Bird fancier's lung
Bird fancier's lung is a type of hypersensitivity pneumonitis caused by bird droppings. The lungs become inflamed with granuloma formation.Bird Fancier's Lung , also called bird-breeder's lung and pigeon-breeder's lung, is a subset of Hypersensitivity pneumonitis...
, farmer's lung
Farmer's lung
Farmer's lung is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mould spores or other agricultural products. It results in a type III hypersensitivity inflammatory response and can progress to become a chronic condition which is considered...
, and bakers lung (See Wheat allergy
Wheat allergy
Wheat allergy is a food allergy, but can also be a contact allergy resulting from occupational exposure. Like all allergies wheat allergy involves IgE and mast cell response. Typically the allergy is limited to the seed storage proteins of wheat, some reactions are restricted to wheat proteins,...
). The third of these theories suggests that pollution (such as diesel exhaust) might be responsible for the increase of these diseases; however, some also claim that developed nations have also been becoming cleaner, and much more so than in the bleak Dickensian years of the early industrial revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
.
For immunological conditions related to Strachan's original version of the hygiene hypothesis, such as atopy
Atopy
Atopy or atopic syndrome is a predisposition toward developing certain allergic hypersensitivity reactions.Atopy may have a hereditary component, although contact with the allergen must occur before the hypersensitivity reaction can develop ....
and asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, the pool chlorine hypothesis
Pool chlorine hypothesis
The pool chlorine hypothesis is the hypothesis that long-term attendance at indoor chlorinated swimming pools by children up to the age of about 6-7 years is a major factor in the rise of asthma in rich countries since the late twentieth century. A narrower version of the hypothesis, i.e...
was proposed by Albert Bernard and his colleagues as an alternative hypothesis based on epidemiological
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
evidence in 2003.
See also
- Hookworm in therapy
- Antibacterial soapAntibacterial soapAntibacterial soap is any cleaning product to which active antibacterial ingredients have been added. These chemicals kill bacteria and microbes, but are no more effective at deactivating viruses than any other kind of soap or detergent, and they also kill nonpathogenic bacteria.-Ingredients:Most...
- Helminthic therapyHelminthic therapyHelminthic therapy, a type of immunotherapy, is the treatment of autoimmune diseases and immune disorders by means of deliberate infestation with a helminth or with the ova of a helminth. Helminths are parasitic worms such as hookworms and whipworms....
(includes more discussion of hygiene hypothesis) - Diseases of affluenceDiseases of affluenceDiseases of affluence is a term sometimes given to selected diseases and other health conditions which are commonly thought to be a result of increasing wealth in a society...