Sunscreen (also known as sunblock or suntan lotion [ Nassau County Health Department [ Jacksonville online] ] ) is a lotion, spray or other topical product that absorbs or reflects the sun's ultraviolet (UV) radiation and protects the skin.

Sunscreens contain one or more UV filters of which there are three main types [Shaath, N. (2005). "The Chemistry of Ultraviolet Filters," in Regulations and Commericial Development 3rd edition, edited by N. Shaath, Taylor and Francis Press, New York. 954pp, 2005.] :
* Organic chemical compounds that absorb ultraviolet light (such as oxybenzone)
* Inorganic particulates that reflect, scatter, and absorb UV light (such as titanium dioxide, zinc oxide), or a combination of both.Clarifyme|date=May 2008
* Organic particulates that mostly absorb light like organic chemical compounds, but contain multiple chromophores, may reflect and scatter a fraction of light like inorganic particulates, and behave differently in formulations than organic chemical compounds.Clarifyme|date=May 2008 An example is Tinosorb M.

Medical organizations such as the American Cancer Society recommend the use of sunscreen because it prevents the squamous cell carcinoma and the basal cell carcinoma. [ [] What You Need To Know About Skin Cancer] However, several epidemiological studies indicate an increased risk of malignant melanoma for the sunscreen user.cite journal |author=Garland C, Garland F, Gorham E |title=Could sunscreens increase melanoma risk? |url= |journal=Am J Public Health |volume=82 |issue=4 |pages=614–5 |year=1992 |pmid=1546792 |issn=] cite journal |author=Westerdahl J; Ingvar C; Masback A; Olsson H |title= Sunscreen use and malignant melanoma | journal= International journal of cancer. Journal international du cancer |volume=87 |pages=145–50 |year=2000 |doi= 10.1002/1097-0215(20000701)87:1<145::AID-IJC22>3.0.CO;2-3 ] cite journal |author=Autier P; Dore J F; Schifflers E; et al |title=Melanoma and use of sunscreens: An EORTC case control study in Germany, Belgium and France |url= |journal=Int. J. Cancer |volume=61 |issue= |pages=749–755 |year=1995|doi=10.1002/ijc.2910610602] cite journal |author=Weinstock, M. A. |title=Do sunscreens increase or decrease melanoma risk: An epidemiologic evaluation |url= |journal=Journal of Investigative Dermatology Symposium Proceedings |volume=4 |issue= |pages= 97–100 |year=1999|doi=10.1038/sj.jidsp.] cite journal |author=Vainio, H., Bianchini, F. |title=Cancer-preventive effects of sunscreens are uncertain |url= |journal=Scandinavian Journal of Work Environment and Health |volume=26 |issue= |pages=529–31 |year=2000 |issn=] cite journal |author=Wolf P, Quehenberger F, Müllegger R, Stranz B, Kerl H. |title=Phenotypic markers, sunlight-related factors and sunscreen use in patients with cutaneous melanoma: an Austrian case-control study |url= |journal=Melanoma Res. |volume=8 |issue=4 |pages=370–378 |year=1998 |pmid=9764814|doi=10.1097/00008390-199808000-00012] cite journal |author=Graham S, Marshall J, Haughey B, Stoll H, Zielezny M, Brasure J, West D. |title=An inquiry into the epidemiology of melanoma |url= |journal=Am J Epidemiol. |volume=122 |issue=4 |pages=606–619 |year=1985|issn=] cite journal |author=Beitner H, Norell SE, Ringborg U, Wennersten G, Mattson B. |title=Malignant melanoma: aetiological importance of individual pigmentation and sun exposure |url= |journal=Br J Dermatol.|volume=122 |issue=1 |pages=43–51 |year=1990 |pmid=2297503|doi=10.1111/j.1365-2133.1990.tb08238.x] Despite these studies no medical association has published recommendations to not use sunblock. Different meta-analysis publications have concluded that the evidence is not yet sufficient to claim a positive correlation between sunscreen use and malignant melanoma. [cite journal |author=Huncharek M, Kupelnick B |title=Use of topical sunscreens and the risk of malignant melanoma: a meta-analysis of 9067 patients from 11 case-control studies |journal=Am J Public Health |volume=92 |issue=7 |pages=1173–7 |year=2002 |month=July |pmid=12084704 |pmc=1447210 |doi= |url=] [cite journal |author=Dennis LK, Beane Freeman LE, VanBeek MJ |title=Sunscreen use and the risk for melanoma: a quantitative review |journal=Ann. Intern. Med. |volume=139 |issue=12 |pages=966–78 |year=2003 |month=December |pmid=14678916 |doi= |url=]


The dose used in FDA sunscreen testing is 2 mg/cm² of exposed skin.] 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 15–30 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. [cite journal |author=Diffey B |title=When should sunscreen be reapplied? | url= |journal=J Am Acad Dermatol |volume=45 |issue=6 |pages=882–5 |year=2001 |pmid=11712033|doi=10.1067/mjd.2001.117385]

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 those sunscreen chemicals which were absorbed into the skin.cite journal|author=Kerry M. Hanson, Enrico Gratton and Christopher J. Bardeen|title=Sunscreen enhancement of UV-induced reactive oxygen species in the skin|doi=10.1016/j.freeradbiomed.2006.06.011|journal=Free Radical Biology and Medicine|year=2006|volume=11|pages=1205] Some studies have shown that people commonly apply only 1/2 to 1/4 of the amount recommended to achieve the rated SPF, and the effective SPF should be downgraded to a square or 4th root of the advertised value. [cite journal |author=Faurschou A, Wulf HC |title=The relation between sun protection factor and amount of suncreen applied in vivo |journal=Br. J. Dermatol. |volume=156 |issue=4 |pages=716–9 |year=2007 |month=Apr |pmid=17493070 |doi=10.1111/j.1365-2133.2006.07684.x |url=]


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. Somewho suggest that "Gletscher Crème" had a sun protection factor of 2.

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.

Measurements of sunscreen protection

Sun protection factor

The SPF of a sunscreen is a laboratory measure of the effectiveness of sunscreen - the higher the SPF, the more protection a sunscreen offers against UV-B (the ultraviolet radiation that causes sunburn). The SPF indicates the time a person with sunscreen applied can be exposed to sunlight before getting sunburn relative to the time a person without sunscreen can be exposed. For example, someone who would burn after 12 minutes in the sun would expect to burn after 120 minutes if protected by a sunscreen with SPF 10. In practice, the protection from a particular sunscreen depends on factors such as:
* The skin type of the user.
* The amount applied and frequency of re-application.
* Activities in which one engages (for example, swimming leads to a loss of sunscreen from the skin).
* Amount of sunscreen the skin has absorbed.

The SPF is an imperfect measure of skin damage because invisible damage and skin aging is also caused by the very common ultraviolet type A, which does not cause reddening or pain. Conventional sunscreen does not block UVA as effectively as it does UVB, and an SPF rating of 30+ may translate to significantly lower levels of UVA protection according to a 2003 studyFact|date=July 2008. According to a 2004 study, UVA also causes DNA damage to cells deep within the skin, increasing the risk of malignant melanomas. [cite journal |author=Berneburg M, Plettenberg H, Medve-König K, Pfahlberg A, Gers-Barlag H, Gefeller O, Krutmann J |title=Induction of the photoaging-associated mitochondrial common deletion in vivo in normal human skin |journal=J Invest Dermatol |volume=122 |issue=5 |pages=1277–83 |year=2004 |pmid=15140232|doi=10.1111/j.0022-202X.2004.22502.x] Even some products labeled "broad-spectrum UVA/UVB protection" do not provide good protection against UVA rays. [ [ Sunscreen—protection or 'snake oil?' - - ] ] The best UVA protection is provided by products that contain zinc oxide, avobenzone, and ecamsule. Titanium dioxide probably gives good protection, but does not completely cover the entire UV-A spectrum. [cite journal |author=Pinnell SR, Fairhurst D, Gillies R, Mitchnick MA, Kollias N |title=Microfine zinc oxide is a superior sunscreen ingredient to microfine titanium dioxide |journal=Dermatol Surg |volume=26 |issue=4 |pages=309–14 |year=2000 |month=Apr |pmid=10759815 |doi= |url=]

Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions are in force in several countries. The United States does not have mandatory, comprehensive sunscreen standards, although a draft rule has been under development since 1978. In the 2007 draft rule, Food and Drug Administration (FDA) proposed to institute the labelling of SPF 50+ for sunscreens offering more protection. This and other measures were proposed to limit unrealistic claims about the level of protection offered (such as "all day protection"). [ [ Questions and Answers on the 2007 Sunscreen Proposed Rule ] ] . In the EU sunscreens are limited to SPF 50+, indicating a SPF of 60 or higher, and Australia's upper limit is 30. []

The SPF can be measured by applying sunscreen to the skin of a volunteer and measuring how long it takes before sunburn occurs when exposed to an artificial sunlight source. In the US, such an in vivo test is required by the FDA. It can also be measured in vitro with the help of a specially designed spectrometer. In this case, the actual transmittance of the sunscreen is measured, along with the degradation of the product due to being exposed to sunlight. In this case, the transmittance of the sunscreen must be measured over all wavelengths in the UV-B range (290–320 nm), along with a table of how effective various wavelengths are in causing sunburn (the "erythemal action spectrum") and the actual intensity spectrum of sunlight (see the figure). Such "in vitro" measurements agree very well with "in vivo"measurements. . [ [ Optometrics products ] ] Numerous methods have been devised for evalaution of UVA and UVB protection The most reliable spectrophotochemical methods eliminate the subjective nature of grading erythema. [Dominique Moyal "How to measure UVA protection afforded by suncreen products"]

Mathematically, the SPF is calculated from measured data as:mathrm{SPF} = frac{int A(lambda) E(lambda)dlambda}{int A(lambda) E(lambda)/mathrm{MPF}(lambda) , dlambda},where E(lambda) is the solar irradiance spectrum, A(lambda) the erythemal action spectrum, and mathrm{MPF}(lambda) the monochromatic protection factor, all functions of the wavelength lambda. The MPF is roughly the inverse of the transmittance at a given wavelength.

The above means that the SPF is not simply the inverse of the transmittance in the UV-B region. If that were true, then applying two layers of SPF 5 sunscreen would be equivalent to SPF 25 (5 times 5). The actual combined SPF is always lower than the square of the single-layer SPF.

Measurements of UVA protection

Persistent Pigment Darkening (PPD), Immediate Pigment Darkening (IPD), Boots Star System, Japanese PA system

The Persistent Pigment Darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring UVB light protection. Originally developed in Japan, it is the preferred method used by manufacturers such as L'Oreal.

Instead of measuring erythema or reddening of the skin, the PPD method uses UVA radiation to cause a permanent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow you to endure 10 times as much UVA as you would without protection. The PPD method is an "in-vivo" test like SPF. In addition, Colipa has introduced a method which is claimed can measure this "in-vitro" and provide parity with the PPD method. [ [ Colipa UVA method] ]

As part of revised guidelines for sunscreens in the EU, there is a requirement to provide the consumer with a minimum level of UVA protection in relation to the SPF. This should be a UVA PF of at least 1/3 of the SPF to carry the UVA seal. The implementation of this seal is in its phase-in period, so a sunscreen without it may already offer this protection. [ [ ] ]

Star rating system

In the UK and Ireland, the Boots star rating system is a proprietary in vitro method used to describe the ratio of UVA to UVB protection offered by sunscreen creams and sprays. Invented by Dr Diffey of the Boots Company in Nottingham, UK, it has been adopted by most companies marketing these products in the UK. The logo and methodology of the test are freely licenced to any manufacturer or brand of sunscreens that wishes to place products on the UK market. It should not be confused with SPF, which is measured with reference to burning and UVB. One-star products provide the least ratio of UVA protection, five-star products are best. The method has recently been revised in the light of the Colipa UVA PF test, and with the new EU recommendations regarding UVA PF. The method still uses a spectrophotometer to measure absorption of UVA vs UVB, the difference stems from a requirement to pre-irradiate samples (where this was not previously required) to give a better indication of UVA protection, and of photostability when the product is used. With the current methodology, the lowest rating is three stars, the highest being five stars.

Active ingredients

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 photodegradation. A chemical stabilizer is included in some sunscreens containing avobenzone to slow its breakdown - examples include formulations containing Helioplex [ [ Neutrogena | How Helioplex Works] ] and AvoTriplex. [ [ Banana Boat AvoTriplex] ] The stability of avobenzone can also be improved by bemotrizinol, [cite journal
title=Photostabilization of Butyl methoxydibenzoylmethane (Avobenzone) and Ethylhexyl methoxycinnamate by Bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter
year=2001| month=Sep| pmid=11594052
author=Chatelain E, Gabard B.
journal=Photochem Photobiol| volume=74(3)| pages=401–6
] octocrylene [ [ DSM Nutritional Products North America - Cosmetics: Basis for Performance - Parsol 340 - Octocrylene] ] and various other photostabilisers.

Some sunscreens also include enzymes like photolyase, which are claimed to be able to repair UV-damaged DNA. [Dagmar Kulms, Birgit Pöppelmann, Daniel Yaroshdagger, Thomas A. Luger, Jean KrutmannDagger and Thomas Schwarz (1999). Nuclear and cell membrane effects contribute independently to the induction of apoptosis in human cells exposed to UVB radiation "PNAS" 96(14):7974-7979]

FDA allowable ingredients

The following are the FDA allowable active ingredients in sunscreens:

Other ingredients approved within the EU [ [ CL1976L0768EN0150010.0001 1..107 ] ] and other parts of the world, [ [ Australian Regulatory Guidelines for OTC Medicines - Chapter 10 ] ] which have not been testedFact|date=August 2008:

Many of the ingredients not approved by the FDA are relatively new and developed to absorb UVA. [ [ Manage Account - Modern Medicine ] ]

Potential health risks

Adverse health effects may be associated with some synthetic compounds in sunscreens. [ [ Experts explore the safety of sunscreen | ] ] In 2007 two studies by the CDC highlighted concerns about the sunscreen chemical oxybenzone (benzophenone-3). They first detected the chemicals in greater than 95% of 2000 Americans tested, and the second found that mothers with high levels of oxybenzone in their bodies were more likely to give birth to underweight baby girls. [ [ CDC: Americans Carry Body Burden of Toxic Sunscreen Chemical | Environmental Working Group ] ]

See also

* Slip-Slop-Slap - famous Australian sun safety advertising jingle
* "Wear Sunscreen" - a column by Mary Schmich in the form of a speech that became a music single and then made into a music video that became viral on the internet
* Indoor tanning lotion
* Sun protective clothing


External links

* [ FDA rulemaking history for sunscreens] : * [ FDA monograph on sunscreen] : * [ FDA monograph on dosing, mechanism of action, and photodegradation of sunscreen (PDF file)]
* [,shop.browse/category_id,46/option,com_virtuemart/Itemid,59/ Make sure your sunscreen has The Skin Cancer Foundation's Seal of Recommendation]
* [ Environmental Working Group: June 2008 Sunscreen Safety Database and Report]
* [ Information on what sunscreens are and how they work from The Skin Cancer Foundation]
* [ Sunscreen protection calculator]
* [ Sun Safety for Babies and Children] University of Florida/IFAS Extension Department of Family, Youth and Community Sciences
* [ Article on UV absorbers not yet approved by the FDA]
* [ Radiation protectants and their CAS registry number]
* [ European Cosmetics ingredient database (CosIng) ]

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