Dirt is unclean matter, especially when in contact with a person's clothes, skin or possessions when they are said to become dirty. Common types of dirt include:

• dust
  Dust
  Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
  
   — a general powder of organic or mineral matter
• filth — foul matter such as excrement
• grime — a black, ingrained dust such as soot
  Soot
  Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
  
  
• soil
  Soil
  Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
  
   — the mix of clay, sand and humus which lies over the bedrock

Exhibitions and studies

A season of artworks and exhibits on the theme of dirt was sponsored by the Wellcome Trust

Wellcome Trust

The Wellcome Trust was established in 1936 as an independent charity funding research to improve human and animal health. With an endowment of around £13.9 billion, it is the United Kingdom's largest non-governmental source of funds for biomedical research...

 in 2011. The centrepiece was an exhibition at the Wellcome Collection

Wellcome Collection

The Wellcome Collection is a museum at 183 Euston Road, London, displaying an unusual mixture of medical artifacts and original artworks exploring 'ideas about the connections between medicine, life and art'. The Collection comprises three public exhibition spaces, an auditorium, events space, cafe...

 showing pictures and histories of notable dirt such as the great dust heaps at Euston

Euston railway station

Euston railway station, also known as London Euston, is a central London railway terminus in the London Borough of Camden. It is the sixth busiest rail terminal in London . It is one of 18 railway stations managed by Network Rail, and is the southern terminus of the West Coast Main Line...

 and King's Cross in the 19th century and the Fresh Kills

Fresh Kills Landfill

The Fresh Kills Landfill was a landfill covering in the New York City borough of Staten Island in the United States. The name comes from the landfill's location along the banks of the Fresh Kills estuary in western Staten Island...

 landfill which was once the world's largest.

Foci

Computer keyboard

Computer keyboard

In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...

s are especially dirty as, on average, they contain 70 times more microbes than a lavatory seat.

Cleaning

When things are dirty they are usually cleaned with solutions like hard surface cleaner

Hard surface cleaner

Hard surface cleaners is a category of cleaning agents comprising mainly aqueous solutions of specialty chemicals that vary with the amount of dirt and the surface being cleaned.-All-purpose cleaners:...

 and other chemicals; much domestic activity is for this purpose — washing

Washing

Washing is one way of cleaning, namely with water and often some kind of soap or detergent. Washing is an essential part of good hygiene and health....

, sweeping

Broom

A broom is a cleaning tool consisting of stiff fibers attached to, and roughly parallel to, a cylindrical handle, the broomstick. It is thus a variety of brush with a long handle. It is commonly used in combination with a dustpan....

 and so forth.

In a commercial setting, a dirty appearance will give a bad impression of a place such as a restaurant. The dirt in such cases may be classified as temporary, permanent and deliberate. Temporary dirt is streaks and detritus that may be removed by ordinary daily cleaning. Permanent dirt is ingrained stains or physical damage which require major renovation to remove. Deliberate dirt is that which results from design decisions such as decor in dirty yellow or grunge

Grunge

Grunge is a subgenre of alternative rock that emerged during the mid-1980s in the American state of Washington, particularly in the Seattle area. Inspired by hardcore punk, heavy metal, and indie rock, grunge is generally characterized by heavily distorted electric guitars, contrasting song...

 styling.

Disposal

As cities developed, arrangements were made for the disposal of dirt. In Britain, the Public Health Act 1875

Public Health Act 1875

The Public Health Act 1875 was established in the United Kingdom to combat filthy urban living conditions, which caused various public health threats, including the spread of many diseases such as cholera and typhus. Reformers wanted to resolve sanitary problems, because sewage was flowing down the...

 required households to place their refuse into a container which could be moved so that it could be carted away. This was the first legal creation of the dustbin.

Health

Modern society is now thought to be excessively clean. Lack of contact with microorganism

Microorganism

A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

s in dirt when growing up is hypothesised

Hygiene hypothesis

In medicine, the Hygiene Hypothesis states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms , and parasites increases susceptibility to allergic diseases by suppressing natural development of the immune system...

 to be the cause of the epidemic of allergies

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...

 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...

. The human 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...

 requires activation and exercise in order to function properly and exposure to dirt may achieve this. For example, the presence of staphylococcus

Staphylococcus

Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....

 bacteria on the surface of the skin regulates the inflammation

Inflammation

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...

 which results from injury.

People and animals may eat dirt

Pica (disorder)

Pica is characterized by an appetite for substances largely non-nutritive . For these actions to be considered pica, they must persist for more than one month at an age where eating such objects is considered developmentally inappropriate...

. This is thought to be caused by mineral deficiency

Mineral deficiency

Mineral deficiency refers to a hypoalimentation of dietary minerals.Examples include:* Zinc deficiency* Iron deficiency* Magnesium deficiency...

 and so the condition is commonly seen in pregnant women

Pregnancy

Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

.

Neurosis

People may become obsessed by dirt and engage in fantasies and compulsive behaviour about it, such as making and eating mud pies. The source of such thinking may be genetic, as the emotion of disgust

Disgust

Disgust is a type of aversion that involves withdrawing from a person or object with strong expressions of revulsion whether real or pretended. It is one of the basic emotions and is typically associated with things that are regarded as unclean, inedible, infectious, gory or otherwise offensive...

is common and a location for it in the brain has been proposed.

External links

• Dirt season at the Wellcome Collection