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Sunscreen (also commonly known as sun screen, sunblock, suntan lotion, sunburn cream, sun cream or block out) is a lotion, spray, gel or other topical product that absorbs or reflects some of the sun's ultraviolet (UV) radiation on the skin exposed to sunlight and thus helps protect against sunburn. Skin-lightening products have sunscreen to protect lightened skin because light skin is more susceptible to sun damage than darker skin. A number of sunscreens have tanning powder to help the skin to darken or tan; however, tanning powder does not provide protection from UV rays.
Depending on the mode of action, sunscreens can be classified into physical sunscreens (i.e., those that reflect the sunlight) or chemical sunscreens (i.e., those that absorb the UV light).
Medical organizations such as the American Cancer Society recommend the use of sunscreen because it aids in the prevention of developing squamous cell carcinomas. Many sunscreens do not block UVA radiation, which does not primarily cause sunburn but can increase the rate of melanoma and photodermatitis. The use of broad-spectrum (UVA/UVB) sunscreens can address this concern. Diligent use of sunscreen can also slow or temporarily prevent the development of wrinkles and sagging skin.
A 2013 study concluded that the diligent, everyday application of sunscreen can slow or temporarily prevent the development of wrinkles and sagging skin. The study involved 900 white people in Australia and required some of them to apply a broad-spectrum sunscreen every day for four and a half years. It found that people who did so had noticeably more resilient and smoother skin than those assigned to continue their usual practices.
In 2008 two studies by the CDC highlighted concerns about the sunscreen chemical oxybenzone (benzophenone-3). The first study detected the chemical in 97% of the 2,500 Americans tested, while the second found that mothers with high levels of oxybenzone in their bodies were more likely to give birth to underweight baby girls. While controversial, oxybenzone does provide broad-spectrum UV coverage, including UVB and short-wave UVA rays.
In 2006 the Therapeutic Goods Administration of Australia carried out a review of sunscreen safety studies and concluded: "There is evidence from isolated cell experiments that zinc oxide and titanium dioxide can induce free radical formation in the presence of light and that this may damage these cells (photo-mutagenicity with zinc oxide). However, this would only be of concern in people using sunscreens if the zinc oxide and titanium dioxide penetrated into viable skin cells. The weight of current evidence is that they remain on the surface of the skin and in the outer dead layer (stratum corneum) of the skin."
Concerns have also been raised about potential vitamin D deficiency arising from prolonged use of sunscreen. Typical use of sunscreen does not usually result in vitamin D deficiency; however, extensive usage may. Sunscreen prevents ultraviolet light from reaching the skin and if properly applied will, under high UV Index conditions, approximately halve vitamin D synthesis; whether the effect is exacerbated under low UV intensity is not yet proven. When the UV Index is greater than 3 (which occurs daily within the tropics and daily during the spring and summer seasons in temperate regions), 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. With longer exposure to UVB rays, an equilibrium is achieved in the skin, and the vitamin degrades as fast as it is generated.
Early civilizations used a variety of plant products to help protect the skin from sun damage. For example, ancient Greeks used olive oil for this purpose, and ancient Egyptians used extracts of rice, jasmine, and lupine plants whose products are still used in skin care today. Zinc oxide paste has also been popular for skin protection for thousands of years.
Early synthetic sunscreens were first used in 1928, and the first major commercial product was brought to market in 1936, introduced by the founder of L'Oreal, French chemist Eugène Schueller. During the same period, Hamilton Sunscreen came to the Australian market in 1932, developed by chemist H. A. Milton Blake.
Among widely used modern sunscreens, one of the earliest was produced in 1944 for the US military by Benjamin Green, an airman and later a pharmacist, as the hazards of sun overexposure became apparent to soldiers in the Pacific tropics at the height of World War II. The product, named 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. Sales boomed when Coppertone improved and commercialized the substance under the Coppertone girl and Bain de Soleil branding in the early 1950s.
In 1946, Swiss chemist Franz Greiter introduced what may have been the first effective modern sunscreen. 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 is still today a marketer of sunscreen products. In 1974, Greiter adapted earlier calculations from Friedrich Ellinger and Rudolf Schulze and introduced the "sun protection factor" (SPF), which has become a worldwide standard for measuring the effectiveness of sunscreen. It has been estimated that Gletscher Crème had a sun protection factor of 2.
Water-resistant sunscreens were introduced in 1977, and recent development efforts have focused on making sunscreen protection both longer-lasting and broader-spectrum, as well as more appealing to use.
The SPF rating is a measure of the fraction of sunburn-producing UV rays blocked. For example, "SPF 15" means that 1/15th of the burning radiation will reach the skin, assuming sunscreen is applied evenly at a thick dosage of 2 milligrams per square centimeter (mg/cm2). A user can determine the effectiveness of a sunscreen "by multiplying the SPF factor by the length of time it takes for him or her to suffer a burn without sunscreen." Thus, if a person develops a sunburn in 10 minutes when not wearing a sunscreen, the same person will prevent sunburn for 150 minutes if wearing a sunscreen with an SPF of 15. It is important to note that sunscreens with higher SPF do not last or remain effective on the skin any longer than lower SPF and must be continually reapplied as directed, usually every two hours.
The SPF is an imperfect measure of skin damage because invisible damage and skin aging are also caused by ultraviolet type A (UVA, wavelength 315–400 or 320–400 nm), which does not primarily cause reddening or pain. Conventional sunscreen blocks very little UVA radiation relative to the nominal SPF; broad-spectrum sunscreens are designed to protect against both UVB and UVA. According to a 2004 study, UVA also causes DNA damage to cells deep within the skin, increasing the risk of malignant melanomas. Even some products labeled "broad-spectrum UVA/UVB protection" do not provide good protection against UVA rays. Titanium dioxide probably gives good protection, but does not completely cover the UVA spectrum, as early 2000s research suggests that zinc oxide is superior to titanium dioxide at wavelengths between 340 and 380 nm.
Owing to consumer confusion over the real degree and duration of protection offered, labeling restrictions are in force in several countries. In the EU, sunscreen labels can only go up to SPF 50+ (initially listed as 30 but soon revised to 50). Australia's Therapeutic Goods Administration increased the upper limit to 50+ in 2012. In the 2007 and 2011 draft rules, the Food and Drug Administration (FDA) proposed a maximum SPF label of 50, to limit unrealistic claims. Others have proposed restricting the active ingredients to an SPF of no more than 50, due to lack of evidence that higher dosages provide more meaningful protection.
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 UVB–UVA range (290–400 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. Numerous methods have been devised for evaluation of UVA and UVB protection. The most-reliable spectrophotochemical methods eliminate the subjective nature of grading erythema.
The ultraviolet protection factor (UPF) is a similar scale developed for rating fabrics for sun protective clothing.
Mathematically, the SPF (or the UPF) is calculated from measured data as
where is the solar irradiance spectrum, the erythemal action spectrum, and the monochromatic protection factor, all functions of the wavelength . 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 UVB 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.
The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring sunburn protection. Originally developed in Japan, it is the preferred method used by manufacturers such as L'Oréal.
Instead of measuring erythema or reddening of the skin, the PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. The PPD method is an in vivo test like SPF. In addition, Colipa has introduced a method that, it is claimed, can measure this in vitro and provide parity with the PPD 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.
A set of final U.S. FDA rules effective from summer 2012 defines the phrase "broad spectrum" as providing UVA protection proportional to the UVB protection.
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. Based on original work by Prof. Brian Diffey at Newcastle University, the Boots Company in Nottingham, UK, developed a standard method that has been adopted by most companies marketing these products in the UK. The logo and methodology of the test are licensed for a token fee to any manufacturer or brand of sunscreens that are sold in the Boots retail chain, provided the products to which the logo is applied perform to the standard claimed. Own Label products exclusively sold in other retailers are now excluded from the terms of the license.
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 versus 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.
In August 2007, the FDA put out for consultation the proposal that a version of this protocol be used to inform users of American product of the protection that it gives against UVA, but after concern this would be too confusing this was not adopted.
Asian brands, particularly Japanese ones, tend to use The Protection Grade of UVA (PA) system to measure the UVA protection a sunscreen provides. The PA system is based on the PPD reaction and is now widely adopted on the labels of sunscreens. According to the Japan Cosmetic Industry Association, PA+ corresponds to a UVA protection factor between two and four, PA++ between four and eight, and PA+++ more than eight.
Sunblock typically refers to opaque sunscreen that is effective at blocking both UVA and UVB rays and uses a heavy carrier oil to resist being washed off. Titanium dioxide and zinc oxide are two of the important ingredients in sunblock. Unlike the organic sun-blocking agents used in many sunscreens, these metal oxides do not degrade with exposure to sunlight.
The use of the word "sunblock" in the marketing of sunscreens is controversial. Since 2013, the FDA has banned such use because it can lead consumers to overestimate the effectiveness of products so labeled. Nonetheless, many consumers use the words sunblock and sunscreen synonymously.
Sunscreens contain one or more of the following 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 and AvoTriplex. The stability of avobenzone can also be improved by bemotrizinol, octocrylene and various other photostabilisers. Most organic compounds in sunscreens slowly degrade and become less effective over the course of several years if stored properly, resulting in the expiration dates calculated for the product.
Sunscreening agents are used in some hair care products such as shampoos, conditioners and styling agents to protect against protein degradation and color loss. Currently, benzophenone-4 and ethylhexyl methoxycinnamate are the two sunscreens most commonly used in hair products. Cinnamidopyltrimonium chloride and a few others are used to a much less degree. The common sunscreens used on skin are rarely used for hair products due to their texture and weight effects.
The following are the FDA allowable active ingredients in sunscreens:
|UV-filter||Other names||Maximum concentration||Permitted in these countries||Results of safety testing|
|p-Aminobenzoic acid||PABA||15% (EU: banned from sale to consumers from 8 October 2009)||USA, AUS||Protects against skin tumors in mice. Shown to increase DNA defects, however, and is now less commonly used.|
|Padimate O||OD-PABA, octyldimethyl-PABA, σ-PABA||8% (EU, USA, AUS) 10% (JP) |
(Not currently supported in EU and may be delisted)
|EU, USA, AUS, JP|
|Phenylbenzimidazole sulfonic acid||Ensulizole, Eusolex 232, PBSA, Parsol HS||4% (US, AUS) 8% (EU) 3% (JP)||EU, USA, AUS, JP||Genotoxic in bacteria|
|Cinoxate||2-Ethoxyethyl p-methoxycinnamate||3% (US) 6% (AUS)||USA, AUS|
|Oxybenzone||Benzophenone-3, Eusolex 4360, Escalol 567||6% (US) 10% (AUS, EU) 5% (JP)||EU, USA, AUS, JP|
|Homosalate||Homomethyl salicylate, HMS||10% (EU, JP) 15% (US, AUS)||EU, USA, AUS, JP|
|Menthyl anthranilate||Meradimate||5%||USA, AUS|
|Octocrylene||Eusolex OCR, 2-Cyano-3,3-diphenyl acrylic acid, 2-ethylhexylester||10%||EU, USA, AUS, JP||Increases ROS|
|Octyl methoxycinnamate||Octinoxate, EMC, OMC, Ethylhexyl methoxycinnamate, Escalol 557, 2-Ethylhexyl-paramethoxycinnamate, Parsol MCX||7.5% (US) 10% (EU, AUS) 20% (JP)||EU, USA, AUS, JP|
|Octyl salicylate||Octisalate, 2-Ethylhexyl salicylate, Escalol 587,||5% (EU, USA, AUS) 10% (JP)||EU, USA, AUS, JP|
|Sulisobenzone||2-Hydroxy-4-Methoxybenzophenone-5-sulfonic acid, 3-Benzoyl-4-hydroxy-6-methoxybenzenesulfonic acid, Benzophenone-4, Escalol 577||5% (EU) 10% (US, AUS, JP)||EU, USA, AUS, JP|
|Trolamine salicylate||Triethanolamine salicylate||12%||USA, AUS|
phenyl)propane-1,3-dione, Butyl methoxy dibenzoylmethane, BMDBM, Parsol 1789, Eusolex 9020
|3% (US) 5% (EU, AUS)10% (JP)||EU, USA, AUS, JP||Not available|
|Ecamsule||Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid||10%||EU, AUS (US: approved in certain formulations up to 3% via New Drug Application (NDA) Route)||Protects against skin tumors in mice|
|Titanium dioxide||CI77891||25% (No limit Japan)||EU, USA, AUS, JP|
|Zinc oxide||25% (US) 20% (AUS) |
(EU: 25%, provided particle size >100 nm) (Japan: no limit)
|EU, USA, AUS, JP||Protects against skin tumors in mice|
|UV-filter||Other names||Maximum concentration||Permitted in|
|4-Methylbenzylidene camphor||Enzacamene, Parsol 5000, Eusolex 6300, MBC||4%*||EU, AUS|
|Tinosorb M||Bisoctrizole, Methylene Bis-Benzotriazolyl Tetramethylbutylphenol, MBBT||10%*||EU, AUS, JP|
|Tinosorb S||Bis-ethylhexyloxyphenol methoxyphenol triazine, Bemotrizinol, BEMT, anisotriazine||10% (EU, AUS) 3% (JP)*||EU, AUS, JP|
|Neo Heliopan AP||Bisdisulizole Disodium, Disodium phenyl dibenzimidazole tetrasulfonate, bisimidazylate, DPDT||10%||EU, AUS|
|Mexoryl XL||Drometrizole Trisiloxane||15%||EU, AUS|
|Benzophenone-9||Uvinul DS 49, CAS 3121-60-6, Sodium Dihydroxy Dimethoxy Disulfobenzophenone ||10%||JP|
|Uvinul T 150||Octyl triazone, ethylhexyl triazone, EHT||5% (EU, AUS) 3% (JP)*||EU, AUS|
|Uvinul A Plus||Diethylamino Hydroxybenzoyl Hexyl Benzoate||10% (EU,JP)||EU, JP|
|Uvasorb HEB||Iscotrizinol, Diethylhexyl butamido triazone, DBT||10% (EU) 5% (JP)*||EU, JP|
|Parsol SLX||Dimethico-diethylbenzalmalonate, Polysilicone-15||10%||EU, AUS, JP|
|Amiloxate||Isopentyl-4-methoxycinnamate, Isoamyl p-Methoxycinnamate, IMC, Neo Heliopan E1000||10%*||EU, AUS|
* Time and Extent Application (TEA), Proposed Rule on FDA approval expected 2009
Many of the ingredients awaiting approval by the FDA were relatively new, and developed to absorb UVA. In 2014, the U.S. Congress introduced the Sunscreen Innovation Act, with the goal of accelerating the FDA approval process.
A sunscreen study from 2001 suggests that the best protection is achieved by dividing the SPF number in half and reapplying that many minutes after sun exposure begins. For example, if the SPF is 30, sunscreen should be reapplied once after 15 minutes of exposure. Further reapplication is only necessary after activities such as swimming, sweating, or rubbing/wiping.
More-recent research at the University of California, Riverside, indicates that sunscreen must 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 that were absorbed into the skin.
The dose used in FDA sunscreen testing is 2 mg/cm2 of exposed skin. If one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32-inch (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. Larger or smaller individuals should scale these quantities accordingly.
Some studies have shown that people commonly apply only 1/2 to 1/4 of the amount recommended for achieving the rated sun protection factor (SPF), and in consequence the effective SPF should be downgraded to a square root or 4th root of the advertised value. A later study found a significant exponential relation between SPF and the amount of sunscreen applied, and the results are closer to linearity than expected by theory.
Sunscreen labeling standards have been evolving in the United States since the FDA first adopted the SPF calculation in 1978. The FDA issued a comprehensive set of rules in June 2011, taking effect in 2012–2013, designed to help consumers identify and select suitable sunscreen products offering protection from sunburn, early skin aging, and skin cancer:
Certain sunscreens in water under ultraviolet light can increase the production of hydrogen peroxide, which damages phytoplankton. Nanoparticles of titanium dioxide, a common ingredient of sunscreens, can accumulate in coastal waters and be ingested by marine animals.