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Sunscreen (also known as sunblock, suntan lotion) is a lotion, spray or other topical product that is supposed to protect the skin from the sun\'s ultraviolet (UV) radiation. The use of sunscreen does reduce sunburn and other skin damages which are caused by direct DNA damage. However other effects of the UV-radiation which are caused by the indirect DNA damage are under certain conditions even amplified by the use of sunscreen. Many epidemiological studies show an increased risk of melanoma for the sunscreen user. Garland C, Garland F, Gorham E (1992). "Could sunscreens increase melanoma risk?". Am J Public Health 82 (4): 614-5. PMID 1546792. Westerdahl J; Ingvar C; Masback A; Olsson H (2000). "Sunscreen use and malignant melanoma.". International journal of cancer. Journal international du cancer 87: 145-50. Other studies contest the idea that sunscreen was the cause of the increasing melanoma incidences.[citation needed].
The photochemical properties of sunscreen ingredients are inferiour to those of melanin, and it is well known in the scientific literature, that those sunscreen molecules that penetrate into the skin will act as a photosensitizer and thereby increase the indirect DNA damage. While it is known, that sunscreen which gets into contact with living tissue is having a damaging effect on this tissue many medical doctors claim, that sunscreen does not pass the epidermal barrier into the human skin.
Sunscreen is a cosmetic product, and no medical benefit has to be shown in order to market it. In Europe and Australia the sunscreen ingredients are not tested by the authorities for photocarcinogenic effects, Lautenschlager, Stephan; Wulf, Hans Christian; Pittelkow, Mark R. (2007). "photoprotection". Lancet 370: 528-37. , however, in the USA the newer formulations are tested for photocarcinogenic effects. The most common ingredients in sunscreens on the market today were introduced before this testing became compulsory.
In the United States, the term suntan lotion refers to lotion designed to moisturize and maximize UV exposure and tanning rather than block it. These are commonly called indoor tanning lotions when designed for use with tanning beds and have no sunscreen in them, or just suntan lotion if designed for outdoor use which may or may not have sunscreen protection in them.
The positive correlation between sunscreen use and an increased melanoma risk is often blamed on the absence of UVA filters in earlier sunscreen formulations. Those scientist who are optimistic about sunscreen use claim that sunscreens which protect against both UVB (ultraviolet radiation with wavelength between 280 and 320 nm) and UVA (between 320 and 400 nm) will result in protection against melanoma as well.
UVB-radiation causes sunburn. UVA - which penetrates the skin more deeply - has more long-term effects, such as premature skin aging. Most sunscreens work by containing either an organic chemical compound that absorbs ultraviolet light (such as oxybenzone) or an opaque material that reflects light (such as titanium dioxide, zinc oxide), or a combination of both. Typically, absorptive materials are referred to as chemical blocks, whereas opaque materials are mineral or physical blocks.
The two effects which cause the rising number of melanomas are explained here: |Sunscreens and Cancer by Hans R Larsen.
Dosing for sunscreen can be calculated using the formula for body surface area and subsequently subtracting the area covered by clothing that provides effective UV protection. The dose used in FDA sunscreen testing is 2 mg/cm2.http://www.fda.gov/ohrms/dockets/dailys/00/Sep00/090600/c000573_10_Attachment_F.pdf Provided one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist, that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz) evenly to the uncovered body area. Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face.
Contrary to the common advice that sunscreen should be reapplied every 2-3 hours, some research has shown that the best protection is achieved by application 30 minutes before exposure, followed by one reapplication 15-30 minutes after the sun exposure begins. Further reapplication is only necessary after activities such as swimming, sweating, and rubbing.Diffey B (2001). "When should sunscreen be reapplied?". J Am Acad Dermatol 45 (6): 882-5. PMID 11712033.
However, more recent research at the University of California, Riverside indicates that sunscreen needs to be reapplied within 2 hours in order to remain effective. Not reapplying could even cause more cell damage than not using sunscreen at all, due to the release of extra free radicals from absorbed chemicals.Hanson Kerry M.; Gratton Enrico; Bardeen Christopher J. (2006). "Sunscreen enhancement of UV-induced reactive oxygen species in the skin". Free Radical Biology and Medicine 41 (8): 1205-1212.
All medical statistics, that have investigated the effect of sunscreen use, have found an increase of malignant melanoma cases associated with sunscreen use. Garland et al. have compared the population of Queensland with the rest of Australia, because in Queensland the use of sunscreen has been promoted the earliest and the strongest compared to the rest of Australia. The increased sunscreen consumption in Queensland has led to a steep rise in the number of melanoma cases. At the time of this study (1992) Queensland had the highest incidence number of melanoma cases in the world. In other parts of Australia the use of sunscreen had been promoted only later, and the melanoma rates increased in these other parts with the same a delay.
Hunter et al. have found a higher risk for skin cancer in women who used sunscreen than in those who did not use sunscreen Hunter D J; Colditz G A; Stampfer M J, et al. (1990). "Risk factors for basal cell carcinoma in a prospective cohort of women.". Ann. Epidemiology 1: 13-23. This higher risk persisted even after multiple adjustments have been made for confounding factors like skin type and the amount of time spend outdoors.
Philippe Autier et al .have performed a case-control study with 418 melanoma cases and 438 healthy controls in France Belgium and Germany. Autier P; Dore J F; Schifflers E; et al (1995). "Melanoma and use of sunscreens: An EORTC case control study in Germany, Belgium and France". Int. J. Cancer 61: 749-755. They have investigated groups of people who had sunburns in their childhood and those who did not, they have investigated those who were aware of health hazards associated with exaggerated UV-exposure and those who were not aware. These corrections were made to account for convoluting factors like childhood sunburns which might trigger sunscreen use and increase skin cancer risks. They found higher risks for melanoma within each group for those individuals that use sunscreen. Thereby they excluded the convoluting factors, and it had been shown, that it is the sunscreen use itself that causes the skin cancer.
They stated that "due to the divorce between public health messages and results from epidemiological studies, prevention programmes should not affirm that sunscreen use prevents cutaneous melanoma."
Furthermore they underlined the importance of truthful information to the public: They found that the regular sunscreen user unaware of the dangers linked to exaggerated UV-exposure have a 12 times higher risk when compared to aware subjects who never use sunscreen.
Within the group of people unaware of the dangers linked to exaggerated UV-exposure the sunscreen users have a 3.36 times higher risk for melanoma than the non-user.
Westerdahl et al. have performed a case-control study on 571 patients with malignant melanoma and 913 healthy controls. All the patients and controls were asked about their history of sunburn, hair color, sunbathing habits (how long, how often) and - of course - use of sunscreen. They had found a significantly elevated risk for developing malignant melanoma associated with regular sunscreen use. Several adjustments were made with respect to the history of sunburns, hair color and other factors. They state that even in two groups that differ neither in sunbathing frequency nor in duration of each sunbathing session an increased risk for melanoma was found for those who always use sunscreen.
The results from the epidemiological studies have lead to lawsuits against sunscreen manufacturers.
Unfortunately all these lawsuits limit themselves to the absence of UV-A filters, even so the absorption of sunscreen into the skin has contributed to the higher melanoma rate in sunscreen users as well (see below).
Arrows indicate a causal connection
It is certainly true that a statistical correlation exists between the number of sunburns and the risk to develop melanoma. This statistical correlation has in the past been interpreted as a causal connection. The medical community took this correlation as an indication that sunburns cause melanoma. This has been shown to be wrong in several studies. Wolf and Kripke have shown that protecting against sunburn does not imply protection against other damaging effects of UV-radiation Wolf P; Donawho C K; Kripke M L (1994). "Effect of Sunscreens on UV radiation-induced enhancements of melanoma in mice.". J. nat. Cancer. Inst. 86: 99-105. Genetic studies have investigated the mutations in the melanoma of skin cancer patients. The mechanism of DNA damage which produced the melanoma can be identified from the kind of mutation, and it was shown that malignant melanoma in healthy humans originate from direct DNA damage only in 8% of the cases and melanoma originate from the indirect DNA damage in 92 % of the cases Davies H.; Bignell G. R.; Cox C.; (6 2002). "Mutations of the BRAF gene in human cancer". Nature 417: 949-954. . Since the direct DNA damage is connected to sunburn it can be said that sunburn causes only 8 % of the melanoma cases and the indirect DNA damage (which is often amplified by sunscreen because it penetrates into the skin) is responsible for 92 % of all melanoma cases.
(Indirect DNA damage is caused by reactive oxygen species (ROS), oxidative stress and free radicals)
There are several contributors to the increased melanoma risk among sunscreen users:
At this time, sunscreen is not tested (in Europe, Japan and Australia) for photocarcinogenic effects before it is released onto the market. In the US such testing became compulsory in 1978, and since then only 3 new substances have managed to fullfill these new requirements - illustrating how difficult it is to create a sunscreen ingredient that is not photocarcinogenic. Even in the US most of the sunscreens that are sold had their ingredients permitted to the market before testing for photocarcinogenic effects became compulsory. Furthermore it is important to know that those tests for photocarcinogenic properties are comparing two test animals that stay in the sun for the same amount of time. And there are other restrictions of these tests as well. For example the animal has not been naked for 100000 years - a time scale that is evolutionary relevant and humans have developed better defense mechanisms than those animals.
In summary the factors that lead to a higher melanoma risk in Sunscreen users are:
Experiments on mice have shown a protective effect of sunscreens against melanoma. The following experiments were performed in 1982, 1985 and 1990 - after this the animal protection policies do not allow animal testing for cosmetic products any more. In these experiments the mice were treated with sunscreen, and then immediately irradiated for only 10 minutes Wulf HC; Poulsen T; Brodthagen H; Hou-Jenson K; (1982). "Sunscreens for delay of ultraviolet induction of skin tumors". J Am Acad Dermatol 7: 194-202. Reeve VE; Greenoak GE; Gallagher CH; Canfield PJ; Wilkinson FJ (1985). "Effect of immunosuppressive agents and sunscreens on UV carcinogenesis in the hairless mouse". Aust J Exp Biol Med Sci 63: 655-655. or for 3 to 7 minutes Flindt-Hansen, HP; Thune P, Larsen, TE (1990). "The inhibiting effect of PABA on photocarcinogenesis". Arch Dermatol Res 282: 38-41. after this time the irradiation stopped and the next sunscreen + irradiation treatment was done after a 2 day break. Within these 10 minutes the sunscreen does not penetrate through the epidermal barrier. For this reason the mice were not affected by the photosensitaziation effect of the sunscreen chemicals as it is described in . Despite the obvious discrepancy between such an experimental design and a real situation of sunscreen use, these experiment have been widely used as arguments to promote the use of sunscreen. Obviously human use has a different time-pattern because most sunscreen users stay in the sun longer than 10 minutes. This longer time allows the sunscreen to diffuse into the skin which leads to free radical generation inside the skin.
Melanin has an extremely efficient photoprotective mechanism that dissipates the energy from the UV-radiation as harmless heat. This property is crucial to avoid the indirect DNA damage. In this mechanism the excited state of the melanin gives of the energy into the vibrational modes of the molecule (heat) by a process that is called internal conversion. This way melanin does not act as a photosensitizer. This photochemical process has been optimized by nature for melanin out of necessity. The internal conversion of melanin is so fast, that more than 99.9 % of the energy is dissipated as heat. Meredith, Paul; Riesz, Jennifer (2004). "Radiative Relaxation Quantum Yields for Synthetic Eumelanin". Photochemistry and photobiology 79 (2): 211-216.
Sunscreen ingredients do not posses this photoprotective property. They do not efficiently dissipate the absorbed energy. In fact many of those chemicals (e.g.: PABA, Benzophenone or Coumarin) are used as photosensitizers in chemical reactions. Coumarin is used as a dye in lasers. The property that makes it suitable for such an application is the long-lived excited state. Exactly this property makes it unsuitable for use in sunscreen. It will act as a photosensitizer starting indirect DNA damage - all the while preventing sunburn. Chemicals with a long lived excited state - substances that are used in chemistry as photosensitizers - should not be used in sunscreens. And yet they are.
The first effective sunscreen may have been developed by chemist Franz Greiter in 1938. The product, called Gletscher Crème (Glacier Cream), subsequently became the basis for the company Piz Buin (named in honor of the place Greiter allegedly obtained the sunburn that inspired his concoction), which today is a well-known marketer of sunscreen products. Some internet articles suggest that Gletscher Crème had a sun protection factor of 2, although a research citation is not readily available online.
The first widely used sunscreen was produced by Benjamin Greene, an airman and later a pharmacist, in 1944. The product, Red Vet Pet (for red veterinary petrolatum), had limited effectiveness, working as a physical blocker of ultraviolet radiation. It was a disagreeable red, sticky substance similar to petroleum jelly. This product was developed during the height of World War II, when it was likely that the hazards of sun overexposure were becoming apparent to soldiers in the Pacific and to their families at home.
Franz Greiter is credited with introducing the concept of Sun Protection Factor (SPF) in 1962, which has become a worldwide standard for measuring the effectiveness of sunscreen when applied at an even rate of 2 milligrams per square centimeter (mg/cm²). Some controversy exists over the usefulness of SPF measurements, especially whether the 2 mg/cm² application rate is an accurate reflection of people’s actual use.
Newer sunscreens have been developed with the ability to withstand contact with water and sweat.
The principal ingredients in sunscreens are usually aromatic molecules conjugated with carbonyl groups. This general structure allows the molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays from reaching the skin. So, upon exposure to UV light, most of the ingredients (with the notable exception of avobenzone) do not undergo significant chemical change, allowing these ingredients to retain the UV absorbing potency without significant photo-degradation.
The following are the FDA allowable active ingredients in sunscreens:
Recently FDA approved:
Others approved within the EUhttp://eur-lex.europa.eu/LexUriServ/site/en/consleg/1976/L/01976L0768-20060809-en.pdf and other parts of the worldhttp://www.tga.gov.au/docs/pdf/argom_10.pdf include:
A lot of the ingredients not approved by the FDA are relatively new and developed to absorb UVA.http://www.modernmedicine.com/modernmedicine/article/articleDetail.jsp?id=169626
The hormone alpha-melanocyte stimulating hormone is made when the body is exposed to sunlight and is responsible for the development of the pigment melanin. Research is being done to create stable artificial forms of the hormone. A promising candidate, melanotan, might be useful in the prevention of skin cancer, by causing tanning without the need for exposure to dangerous levels of UV.
Some individuals can have mild to moderate allergic reactions to certain ingredients in sunscreen, particularly the chemical benzophenone, which is also known as phenyl ketone, diphenyl ketone, or benzoylbenzene. It is not clear how much of benzophenone is absorbed into the bloodstream, but trace amounts can be found in urinalysis after use.
Sunscreens are effective in reducing sunburn, but not necessarily the risk of cancer. A study published in April 1992, entitled "Could sunscreens increase melanoma risk?" reported that the greatest increase in melanoma occurred in those regions where sunscreen use is most prevalent.Garland C, Garland F, Gorham E (1992). "Could sunscreens increase melanoma risk?". Am J Public Health 82 (4): 614-5. PMID 1546792. The authors point out that "the SPF of sunscreens concerns solely their ability to absorb ultraviolet B (UVB) light. Even sunscreens with high SPF factors can be completely transparent to ultraviolet A (UVA), which includes 90 to 95% of ultraviolet light. UVA blocking ingredients, which have commonly been added to most sunscreens since 1989, block only half the UVA spectrum and provide a protection factor against delayed UVA induced erythema of only 1.7 at usual concentrations. Both UVA and UVB have been shown to mutate DNA and promote skin cancers in animals. UVA also penetrates deeper into the skin than UVB... two studies suggest that sunscreens may not be effective in preventing skin cancer. A large case-control study showed higher risks of melanoma in men who used sunscreens, and a large prospective study showed a higher incidence of basal cell carcinoma in women who used sunscreens."
Recently, there has been increased attention to the possibility of adverse health effects associated with the synthetic compounds in most sunscreens. http://www.straight.com/content.cfm?id=18501 Recent studies found that some sunscreens generate harmful compounds that might promote skin cancer. The three commonly used ultraviolet (UV) filters -- octylmethoxycinnamate, benzophenone 3, and octocrylene -- eventually soak into the deeper layers of the skin after their application, where they act as photosensitizer and thereby amplify the free radical production from UV-light (indirect DNA damage). UV rays absorbed by the skin can generate harmful compounds called reactive oxygen species (ROS), which can cause skin cancer and premature aging. The researchers found that once the filters in sunscreen soak into the lower layers of skin, the filters react with UV light to create more damaging ROS. To reduce ROS generation and damage, the researchers recommend reapplying the sunscreen often, which will replenish the sunscreen which has penetrated the skin. Future possibilities may include the development of sunscreens which stay at the surface of the skin, or mixing sunscreens with antioxidants that can neutralize ROS.http://www.newsroom.ucr.edu/cgi-bin/display.cgi?id=1399
A significant reduction in sun exposure inhibits the production of vitamin D. The use of sunscreen with a sun protection factor (SPF) of 8 inhibits more than 95% of vitamin D production in the skin.Holick M (2004). "Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease". Am J Clin Nutr 80 (6 Suppl): 1678S-88S. PMID 15585788. However, excessive sun exposure has been conclusively linked to some forms of skin cancer and signs of premature aging. Season, geographic latitude, time of day, cloud cover, smog, skin type, and sunscreen all have an effect on vitamin D production in the skin.Holick M (1995). "Environmental factors that influence the cutaneous production of vitamin D". Am J Clin Nutr 61 (3 Suppl): 638S-645S. PMID 7879731. Fifteen minutes per day of direct exposure to the sun (i.e. without sunscreen) is a generally accepted guideline to follow for optimum vitamin D production.Dietary Supplement Fact Sheet: Vitamin D. National Institutes of Health. Retrieved on 2006-06-10.
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