Sunscreen controversy
Encyclopedia
Sunscreen
protects against two common forms of skin cancer, squamous cell carcinoma
(SCC) and basal cell carcinoma
(BCC), and several sunscreen ingredients protect against tumor development in photocarcinogenicity tests in mice. However, there is some evidence, largely arising from correlational studies and in vitro
experiments, that particular sunscreen ingredients (such as oxybenzone
, benzophenone
, octocrylene
, or octyl methoxycinnamate
) may be linked to increased risks of malignant melanoma, a rarer but more deadly form of skin cancer. It has also been linked to vitamin D
deficiency. The broad areas of concern are:
This has led to a sunscreen controversy within the academic community. It is known that some sunscreens only protect against UVB radiation, and not against the more dangerous UVA component of the spectrum. In 2006, a number of class-action lawsuits alleged that sunscreen manufacturers misled consumers into believing that these products provided full sun protection. The lawsuits were settled in 2009. The vitamin D hypothesis is not as widely accepted but continues to generate scholarly debate. Most health authorities and medical associations have concluded that on the whole, sunscreen use is beneficial.
has been found more frequently in sunscreen users compared to non-users in some studies. Other studies found fair skinned people used more suncreen and had more skin cancer, but did not address cause and effect. A meta-analysis of 9067 patients from 11 case–control studies found no association between sunscreen use and development of malignant melanoma. It was suggested that sunscreens block the natural warnings and adaptations mediated by UVB, but allow damage from UVA to go unchecked.
However, these claims could not be supported in three meta-analyses. (Huncharek and Kupelnick, 2000, Annals Epidemiol. vol. 10, p. 467.)
The only evidence suggesting a relationship between sunscreen and melanoma is correlational, and thus cannot be used to establish a causal relationship.
Even though it is rare, malignant melanoma is responsible for 75% of all skin cancer-related death cases, making it the most lethal form of skin cancer. Many scientists argue that the sun-avoiding health message does increase some forms of skin cancer.
There is a correlation
between high UV exposure, especially during childhood, and the risk to develop melanoma, resulting in a WHO recommendation for persons under 18 to avoid sunbed
s.
PABA
causes DNA damage in human cells. PABA was banned as a sunscreen ingredient several years after these findings were published. Phenylbenzimidazole
(PBI) causes DNA photodamage when illuminated while in contact with bacteria or human keratinocyte
s.
Some sunscreen ingredients generate reactive oxygen species
(ROS) when exposed to UVA, which can increase carbonyl formation in albumin and damage DNA. It is also well-known that DNA alterations are necessary for cancer to occur.
Many sunscreen ingredients generate singlet oxygen
under illumination. Several popular UV-filters have been demonstrated to generate free radicals.
Kerry Hanson, et al. have shown for the three sunscreen ingredients octocrylene
, octylmethoxycinnamate
, and benzophenone-3 that after the sunscreen chemicals had time to absorb into the skin the number of ROS and free radicals is higher for the sunscreen user than for the non-user. Such an increase in ROS might increase the chance of melanoma, but this hypothesis has not been tested.
Studies have found that titanium dioxide nanoparticles cause genetic damage in mice, suggesting that humans may be at risk of cancer or genetic disorders resulting from exposure.
DNA, in particular, is susceptible to damage caused by photo-excited compounds.
The absorption of the sunscreen ingredients into the skin does not occur instantaneously, but the sunscreen concentration in the deeper levels of the skin increases over time. For this reason the amount of time between the topical application of sunscreen and the end of the illumination period is an important parameter in experimental studies. Illumination of those sunscreen chromophores which have penetrated the stratum corneum amplifies the generation of ROS.
. The study included 60 transplant
patients who received immunosuppression
, a group of persons with a particularly high risk to develop skin cancer. The patients were very compliant, using sunscreen 5.6 days per week on average. The control group was recruited retrospectively
and consisted of 60 transplant patients equally matched for age, skin type and kind of transplant organ. The control group had been instructed to use sunscreen as well, but were not provided with cost-free sunscreen and showed very poor compliance.
After 24 months, the sunscreen group showed a 53% reduction of actinic keratosis, while the control group showed an increase of 38%. The difference in the development of SCC and BCC were also highly significant. Non-significant results included a slight decrease of herpes and wart
s and a slight increase in acne
in the sunscreen group.
In 2011, Australian researchers found that the regular application of sunscreen with a sun protection factor of 15 or more during a 5-year treatment period reduced the incidence of new primary melanomas during a subsequent 10-year follow-up period.. However the accompanying editorial found the statistics unconvincing. In May 2011 the same journal (Journal of Clinical Oncology) published an alternative analysis of the same data entitled Increased Melanoma After Regular Sunscreen Use? which found that the areas of the skin which had been treated with sunscreen had non-significantly more melanomas than the untreated controls.
These lawsuits limit themselves to the absence of UV-A filters.
In August 2007, the United States Food and Drug Administration tentatively concluded that "the available evidence fails to show that sunscreen use alone prevents skin cancer[...]"
Sunscreen ingredients are not tested in Europe, Japan or Australia for photocarcinogenic effects before being introduced to the market. Even in the US, most sunscreens sold in 2008 have not passed regulatory testing either, due to a grandfather clause
. Three new sunscreen active ingredients introduced in the US since 1978 have fulfilled new testing requirements.
production in the skin. Recent studies showed that, following the successful "Slip-Slop-Slap
" health campaign encouraging Australians to cover up when exposed to sunlight to prevent skin cancer
, an increased number of Australians and New Zealanders became vitamin D deficient. Ironically, there are indications that vitamin D deficiency may lead to skin cancer. To avoid vitamin D deficiency, vitamin supplements can be taken. Adequate amounts of vitamin D3 can be made in the skin after only ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen. This applies in sunlight when the UV index is greater than 3, which occurs daily within the tropics and during the spring and summer seasons in temperate regions. With sunscreen, the required exposure would be longer: if 95% of vitamin D production is inhibited, then it proceeds at only 5%, or 1/20th, the normal rate, and it would take 20 times as long—200 to 300 minutes (3-1/3 to 5 hours), twice a week—of sun exposure to the face, arms, hands, or back for adequate vitamin D to be made in the skin. Obviously, the required time would decrease with increased body exposure area, as when wearing a swimsuit on a beach, a very common setting where sunscreen is used. By this math, it is apparent that vacationers who spend hours on the beach each day with sunscreen on may make more vitamin D in a week of vacation than they do during a typical week in their lives with no sunscreen, if they spend most of their non-vacationing time inside houses, offices, and other buildings where they get almost no sun exposure. Also, it is worth noting that with longer exposure to UVB rays, an equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is generated. Vitamin D overdose is nearly impossible from natural sources, including food sources.
Sunscreen
Sunblock is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet radiation on the skin exposed to sunlight and thus helps protect against sunburn...
protects against two common forms of skin cancer, squamous cell carcinoma
Squamous cell carcinoma
Squamous cell carcinoma , occasionally rendered as "squamous-cell carcinoma", is a histologically distinct form of cancer. It arises from the uncontrolled multiplication of malignant cells deriving from epithelium, or showing particular cytological or tissue architectural characteristics of...
(SCC) and basal cell carcinoma
Basal cell carcinoma
Basal-cell carcinoma is the most common type of skin cancer. It rarely metastasizes or kills. However, because it can cause significant destruction and disfigurement by invading surrounding tissues, it is still considered malignant. Statistically, approximately 3 out of 10 Caucasians may develop a...
(BCC), and several sunscreen ingredients protect against tumor development in photocarcinogenicity tests in mice. However, there is some evidence, largely arising from correlational studies and in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
experiments, that particular sunscreen ingredients (such as oxybenzone
Oxybenzone
Oxybenzone is an organic compound used in sunscreens. It forms colorless crystals that are readily soluble in most organic solvents. A 2008 study by the US Centers for Disease Control and Prevention found the compound to be present in 96.8% of human urine samples analyzed as part of the...
, benzophenone
Benzophenone
Benzophenone is the organic compound with the formula 2CO, generally abbreviated Ph2CO. Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone.-Uses:...
, octocrylene
Octocrylene
Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of a diphenylcyanoacrylate with 2-ethylhexanol...
, or octyl methoxycinnamate
Octyl methoxycinnamate
Octyl methoxycinnamate or octinoxate , trade names Eusolex 2292 and Uvinul MC80, is an organic compound that is an ingredient in some sunscreens and lip balms. It is an ester formed from methoxycinnamic acid and 2-ethylhexanol...
) may be linked to increased risks of malignant melanoma, a rarer but more deadly form of skin cancer. It has also been linked to vitamin D
Vitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
deficiency. The broad areas of concern are:
- potentially carcinogenic properties of some sunscreen ingredients
- vitamin D deficiency caused by reduced exposure to ultraviolet light
- incomplete protection against the full ultraviolet spectrum combined with increased time spent in the sun
This has led to a sunscreen controversy within the academic community. It is known that some sunscreens only protect against UVB radiation, and not against the more dangerous UVA component of the spectrum. In 2006, a number of class-action lawsuits alleged that sunscreen manufacturers misled consumers into believing that these products provided full sun protection. The lawsuits were settled in 2009. The vitamin D hypothesis is not as widely accepted but continues to generate scholarly debate. Most health authorities and medical associations have concluded that on the whole, sunscreen use is beneficial.
Studies of melanoma rates
Malignant melanomaMelanoma
Melanoma is a malignant tumor of melanocytes. Melanocytes are cells that produce the dark pigment, melanin, which is responsible for the color of skin. They predominantly occur in skin, but are also found in other parts of the body, including the bowel and the eye...
has been found more frequently in sunscreen users compared to non-users in some studies. Other studies found fair skinned people used more suncreen and had more skin cancer, but did not address cause and effect. A meta-analysis of 9067 patients from 11 case–control studies found no association between sunscreen use and development of malignant melanoma. It was suggested that sunscreens block the natural warnings and adaptations mediated by UVB, but allow damage from UVA to go unchecked.
However, these claims could not be supported in three meta-analyses. (Huncharek and Kupelnick, 2000, Annals Epidemiol. vol. 10, p. 467.)
The only evidence suggesting a relationship between sunscreen and melanoma is correlational, and thus cannot be used to establish a causal relationship.
Even though it is rare, malignant melanoma is responsible for 75% of all skin cancer-related death cases, making it the most lethal form of skin cancer. Many scientists argue that the sun-avoiding health message does increase some forms of skin cancer.
There is a correlation
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
between high UV exposure, especially during childhood, and the risk to develop melanoma, resulting in a WHO recommendation for persons under 18 to avoid sunbed
Sunbed
A sunbed , tanning bed or sun tanning bed is a device which emits ultraviolet radiation to produce a cosmetic tan. Regular tanning beds use several fluorescent lamps that have phosphor blends designed to emit UV in a spectrum that is somewhat similar to the sun...
s.
Alternative view
Authors who claim that sunscreen use causes melanoma have speculated that this occurs by one of the following mechanisms:- the absence of UVA filters combined with a longer exposure time of the sunscreen user
- By reducing the exposure of the skin to UVB radiation, sunscreen suppresses the skin's production of the natural photoprotectant, melanin, and the lack of melanin leads to an increased risk of melanoma.
- free radical generation by sunscreen chemicals that have penetrated into the skin.
- pathogenic cytotoxicity and carcinogenicity of micronized titanium or zinc oxide nanoparticles.
- Retinyl palmitate, a form of Vitamin A that is an ingredient in some sunscreens, may encourage tumor growth in animals http://www.ewg.org/2010sunscreen/full-report/new-fda-study-sunscreen-additive-may-speed-cancer-growth/
Sunscreen ingredients can damage DNA
Some sunscreen ingredients may damage cells when illuminated.PABA
4-Aminobenzoic acid
4-Aminobenzoic acid is an organic compound with the formula H2NC6H4CO2H. PABA is a white grey crystalline substance that is only slightly soluble in water...
causes DNA damage in human cells. PABA was banned as a sunscreen ingredient several years after these findings were published. Phenylbenzimidazole
Phenylbenzimidazole sulfonic acid
Phenylbenzimidazole sulfonic acid is a common sunscreen agent. In 1999, the United States Food and Drug Administration regulated that the name ensulizole be used on sunscreen labels in the United States. Phenylbenzimidazole sulfonic acid is primarily a UVB protecting agent providing only minimal...
(PBI) causes DNA photodamage when illuminated while in contact with bacteria or human keratinocyte
Keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
s.
Some sunscreen ingredients generate reactive oxygen species
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....
(ROS) when exposed to UVA, which can increase carbonyl formation in albumin and damage DNA. It is also well-known that DNA alterations are necessary for cancer to occur.
Many sunscreen ingredients generate singlet oxygen
Singlet oxygen
Singlet oxygen is the common name used for the diamagnetic form of molecular oxygen , which is less stable than the normal triplet oxygen. Because of its unusual properties, singlet oxygen can persist for over an hour at room temperature, depending on the environment...
under illumination. Several popular UV-filters have been demonstrated to generate free radicals.
Kerry Hanson, et al. have shown for the three sunscreen ingredients octocrylene
Octocrylene
Octocrylene is an organic compound used as an ingredient in sunscreens and cosmetics. It is an ester formed by the condensation of a diphenylcyanoacrylate with 2-ethylhexanol...
, octylmethoxycinnamate
Octyl methoxycinnamate
Octyl methoxycinnamate or octinoxate , trade names Eusolex 2292 and Uvinul MC80, is an organic compound that is an ingredient in some sunscreens and lip balms. It is an ester formed from methoxycinnamic acid and 2-ethylhexanol...
, and benzophenone-3 that after the sunscreen chemicals had time to absorb into the skin the number of ROS and free radicals is higher for the sunscreen user than for the non-user. Such an increase in ROS might increase the chance of melanoma, but this hypothesis has not been tested.
Studies have found that titanium dioxide nanoparticles cause genetic damage in mice, suggesting that humans may be at risk of cancer or genetic disorders resulting from exposure.
DNA, in particular, is susceptible to damage caused by photo-excited compounds.
Sunscreen ingredients penetrate the skin
Between 1% and 10% of some sunscreen ingredients are absorbed into the body through the skin.The absorption of the sunscreen ingredients into the skin does not occur instantaneously, but the sunscreen concentration in the deeper levels of the skin increases over time. For this reason the amount of time between the topical application of sunscreen and the end of the illumination period is an important parameter in experimental studies. Illumination of those sunscreen chromophores which have penetrated the stratum corneum amplifies the generation of ROS.
Animal experiments
All studies except for one have found that sunscreens protect mice against melanoma.Clinical study
In 2008, a clinical study showed that the application of sunscreen prevents SCC, BCC and actinic keratosisActinic keratosis
Actinic keratosis is a premalignant condition of thick, scaly, or crusty patches of skin. It is more common in fair-skinned people. It is associated with those who are frequently exposed to the sun, as it is usually accompanied by solar damage...
. The study included 60 transplant
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
patients who received immunosuppression
Immunosuppression
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immuno-suppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse reaction to treatment of other...
, a group of persons with a particularly high risk to develop skin cancer. The patients were very compliant, using sunscreen 5.6 days per week on average. The control group was recruited retrospectively
Medical history
The medical history or anamnesis of a patient is information gained by a physician by asking specific questions, either of the patient or of other people who know the person and can give suitable information , with the aim of obtaining information useful in formulating a diagnosis and providing...
and consisted of 60 transplant patients equally matched for age, skin type and kind of transplant organ. The control group had been instructed to use sunscreen as well, but were not provided with cost-free sunscreen and showed very poor compliance.
After 24 months, the sunscreen group showed a 53% reduction of actinic keratosis, while the control group showed an increase of 38%. The difference in the development of SCC and BCC were also highly significant. Non-significant results included a slight decrease of herpes and wart
Wart
A wart is generally a small, rough growth, typically on a human’s hands or feet but often other locations, that can resemble a cauliflower or a solid blister. They are caused by a viral infection, specifically by human papillomavirus 2 and 7. There are as many as 10 varieties of warts, the most...
s and a slight increase in acne
Acne
Acne is a general term used for acneiform eruptions. It is usually used as a synonym for acne vulgaris, but may also refer to:*Acne aestivalis*Acne conglobata*Acne cosmetica*Acne fulminans*Acne keloidalis nuchae*Acne mechanica...
in the sunscreen group.
In 2011, Australian researchers found that the regular application of sunscreen with a sun protection factor of 15 or more during a 5-year treatment period reduced the incidence of new primary melanomas during a subsequent 10-year follow-up period.. However the accompanying editorial found the statistics unconvincing. In May 2011 the same journal (Journal of Clinical Oncology) published an alternative analysis of the same data entitled Increased Melanoma After Regular Sunscreen Use? which found that the areas of the skin which had been treated with sunscreen had non-significantly more melanomas than the untreated controls.
Social impact
Lawsuits have been filed against sunscreen manufacturers.These lawsuits limit themselves to the absence of UV-A filters.
In August 2007, the United States Food and Drug Administration tentatively concluded that "the available evidence fails to show that sunscreen use alone prevents skin cancer[...]"
Sunscreen ingredients are not tested in Europe, Japan or Australia for photocarcinogenic effects before being introduced to the market. Even in the US, most sunscreens sold in 2008 have not passed regulatory testing either, due to a grandfather clause
Grandfather clause
Grandfather clause is a legal term used to describe a situation in which an old rule continues to apply to some existing situations, while a new rule will apply to all future situations. It is often used as a verb: to grandfather means to grant such an exemption...
. Three new sunscreen active ingredients introduced in the US since 1978 have fulfilled new testing requirements.
Sunscreen and vitamin D
The use of sunscreen with a sun protection factor (SPF) of 8 inhibits more than 95% of vitamin DVitamin D
Vitamin D is a group of fat-soluble secosteroids. In humans, vitamin D is unique both because it functions as a prohormone and because the body can synthesize it when sun exposure is adequate ....
production in the skin. Recent studies showed that, following the successful "Slip-Slop-Slap
Slip-Slop-Slap
Slip-Slop-Slap and wrap is the iconic and internationally recognised sun protection campaign prominent in Australia during the 1980s. Launched by Cancer Council Victoria in 1980, the Slip! Slop! Slap! campaign features a singing, dancing Sid Seagull encouraging people to reduce sun exposure and...
" health campaign encouraging Australians to cover up when exposed to sunlight to prevent skin cancer
Skin cancer
Skin neoplasms are skin growths with differing causes and varying degrees of malignancy. The three most common malignant skin cancers are basal cell cancer, squamous cell cancer, and melanoma, each of which is named after the type of skin cell from which it arises...
, an increased number of Australians and New Zealanders became vitamin D deficient. Ironically, there are indications that vitamin D deficiency may lead to skin cancer. To avoid vitamin D deficiency, vitamin supplements can be taken. Adequate amounts of vitamin D3 can be made in the skin after only ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen. This applies in sunlight when the UV index is greater than 3, which occurs daily within the tropics and during the spring and summer seasons in temperate regions. With sunscreen, the required exposure would be longer: if 95% of vitamin D production is inhibited, then it proceeds at only 5%, or 1/20th, the normal rate, and it would take 20 times as long—200 to 300 minutes (3-1/3 to 5 hours), twice a week—of sun exposure to the face, arms, hands, or back for adequate vitamin D to be made in the skin. Obviously, the required time would decrease with increased body exposure area, as when wearing a swimsuit on a beach, a very common setting where sunscreen is used. By this math, it is apparent that vacationers who spend hours on the beach each day with sunscreen on may make more vitamin D in a week of vacation than they do during a typical week in their lives with no sunscreen, if they spend most of their non-vacationing time inside houses, offices, and other buildings where they get almost no sun exposure. Also, it is worth noting that with longer exposure to UVB rays, an equilibrium is achieved in the skin, and the vitamin simply degrades as fast as it is generated. Vitamin D overdose is nearly impossible from natural sources, including food sources.