tube of factor 15 sun block lotion
Sunscreen (also commonly known as sunblock[1] or sun cream[2]) 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 susceptible to sun damage. Meanwhile, sunscreen products have skin whitening ingredient.
Sunscreens contain one or more UV filters of which there are three main types:[3]
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.[4] However, the use of sunscreens is controversial for various reasons. Many do not block UVA radiation, which does not cause sunburn but can increase the rate of melanoma (another kind of skin cancer), so people using sunscreens may be getting too much UVA without realizing it. Additionally, sunscreens block UVB, and if used consistently this can cause a deficiency of vitamin D.
Dosing
The dose used in FDA sunscreen testing is 2 mg/cm² of exposed skin.[5] 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. Larger individuals should scale these quantities accordingly.
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, or rubbing/wiping.[6]
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.[7] Some studies have shown that people commonly apply only 1/2 to 1/4 of the amount recommended to achieve the rated SPF, and in consequence the effective SPF should be downgraded to a square or 4th root of the advertised value.[8]
George Zachariadis and E Sahanidou of the Laboratory of Analytical Chemistry, at Aristotle University, in Thessaloniki, Greece,have now carried out an inductively coupled plasma atomic emission spectrometric (ICP-AES) analysis in a multi-element assessment of several commercially available sunscreen creams and lotions. "The objective was the simultaneous determination of titanium and several minor, trace or toxic elements (aluminium, zinc, magnesium, iron, manganese, copper, chromium, lead, and bismuth) in the final products," the researchers say. They concluded that "Most of the commercial preparations that were studied showed generally good agreement to the ingredients listed on the product label". However, they also point out that the quantitative composition of the products tested cannot be assessed because the product labels usually do not provide a detailed break down of all ingredients and their concentrations. They also point out that worryingly, their tests consistently revealed the presence of elements not cited in the product formulation, which emphasised the need for a standardised and official testing method for multi-element quality control of these products.[9]
History
The first effective sunscreen may have been developed by chemist Will Baltzer 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[who?] 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. Sales of this product boomed when Coppertone acquired the patent and marketed the substance under the Coppertone girl and Bain de Soleil branding in the early 1950s.
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 is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, relative to the amount required without the sunscreen.[10] So, wearing a sunscreen with SPF 50, your skin will not burn until it has been exposed to 50 times the amount of solar energy that would normally cause it to burn. The amount of solar energy you are exposed to depends not only on the amount of time you spend in the sun, but also the time of day. This is because, during early morning and late afternoon, the sun's radiation must pass through more of the Earth's atmosphere before it gets to you. 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 are also caused by ultraviolet type A (UVA, wavelength 320 to 400 nm), which does not 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.[11][12][13] According to a 2004 study, UVA also causes DNA damage to cells deep within the skin, increasing the risk of malignant melanomas.[14] Even some products labeled "broad-spectrum UVA/UVB protection" do not provide good protection against UVA rays.[15] 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, as recent research suggests that zinc oxide is superior to titanium dioxide at wavelengths between 340 and 380 nm.[16]
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+ (actually indicating a SPF of 60 or higher)[17] while Australia's upper limit is 30+ [18]. 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").[19]
UV-B sunlight spectrum (on a summer day in the Netherlands), along with the CIE Erythemal action spectrum. The effective spectrum is the product of the former two.
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.[20] Numerous methods have been devised for evaluation of UVA and UVB protection The most reliable spectrophotochemical methods eliminate the subjective nature of grading erythema.[21]
Mathematically, the SPF is calculated from measured data as
where E(λ) is the solar irradiance spectrum, A(λ) the erythemal action spectrum, and MPF(λ) the monochromatic protection factor, all functions of the wavelength λ. 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)
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 persistent 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, it is claimed, can measure this in vitro and provide parity with the PPD method.[22]
The UVA seal used in the
EU
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.[23]
Immediate Pigment Darkening (IPD)
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. Based on original work by Prof. Brian Diffey at Newcastle University, the Boots Company in Nottingham, UK, developed a standard method which has been adopted by most companies marketing these products in the UK. The logo and methodology of the test are licenced for a token fee to any manufacturer or brand of sunscreens that wishes to use it, provided the products to which the logo is applied perform to the standard claimed. 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.
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 [24]
Potential health risks
As a defense against UV radiation, the amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present and triggers the release of the melanin from melanocytes. UVB on the other hand yields a tan that takes roughly 2 days to develop because it stimulates the body to produce more melanin. The photochemical properties of melanin make it an excellent photoprotectant.
Sunscreen chemicals on the other hand cannot dissipate the energy of the excited state as efficiently as melanin and therefore the penetration of sunscreen ingredients into the lower layers of the skin increases the amount of free radicals and reactive oxygen species (ROS's).[7]
Some sunscreen lotions now include compounds such as titanium dioxide which helps protect against UVA rays. Other UVA blocking compounds found in sunscreen include zinc oxide and avobenzone. Cantaloupe extract, rich in the compound superoxide dismutase (SOD), can be bound with gliadin to form glisodin, an orally-effective protectant against UVB radiation. There are also naturally occurring compounds found in rainforest plants that have been known to protect the skin from UV radiation damage, such as the fern Phlebodium aureum.
Some sunscreen chemicals produce potentially harmful substances if they are illuminated while in contact with living cells.[25][26][27] The amount of sunscreen which penetrates through the stratum corneum may or may not be large enough to cause damage. In one study of sunscreens, the authors write:
The question whether UV filters acts on or in the skin has so far not been fully answered. Despite the fact that an answer would be a key to improve formulations of sun protection products, many publications carefully avoid addressing this question.[28]
In an experiment by Hanson et al. that was published in 2006, the amount of harmful reactive oxygen species was measured in untreated and in sunscreen-treated skin. In the first 20 minutes the film of sunscreen had a protective effect and the number of ROS species was smaller. After 60 minutes, however, the amount of absorbed sunscreen was so high that the amount of ROS was higher in the sunscreen-treated skin than in the untreated skin.[7]
Some epidemiological studies indicate an increased risk of malignant melanoma for the sunscreen user.[29][30][31][32][33][34][35][36] 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.[37][38]
Adverse health effects may be associated with some synthetic compounds in sunscreens.[39] In 2007 two studies by the CDC highlighted concerns about the sunscreen chemical oxybenzone (benzophenone-3). The first detected the chemicals in greater than 95% of 2000 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.[40]
The use of sunscreen also interferes with vitamin D production, leading to deficiency in Australia after a government campaign to increase sunscreen use.[41] Doctors recommend spending small amounts of time in the sun without sun protection to ensure adequate production of vitamin D.[42] 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 simply degrades as fast as it is generated.[43]
Concerns have been raised regarding the use of nanoparticles in sunscreen.[44] Theoretically, sunscreen nanoparticles could increase rates of certain cancers, or diseases similar to those caused by asbestos.[45] In 2006 the The Therapeutic Goods Administration of Australia concluded a study and found:
"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." [44]
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.[5] A chemical stabilizer is included in some sunscreens containing avobenzone to slow its breakdown - examples include formulations containing Helioplex[46] and AvoTriplex.[47] The stability of avobenzone can also be improved by bemotrizinol,[48] octocrylene[49] and various other photostabilisers.
Some sunscreens also include enzymes like photolyase, which are claimed to be able to repair UV-damaged DNA.[50]
FDA allowable ingredients
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% (5% EC-will be banned from sale to consumers from 8 October 2009) |
EC, USA, AUS |
Protects against skin tumors in mice.[51][52][53] Shown to increase DNA defects, however, and is now less commonly used. |
| Padimate O |
OD-PABA, octyldimethyl-PABA, σ-PABA |
8% (EC,USA,AUS) 10% (JP)
(Not currently supported in EU and may be delisted)
|
EC, USA, AUS, JP |
Not tested |
| Phenylbenzimidazole sulfonic acid |
Ensulizole, Eusolex 232, PBSA, Parsol HS |
4% (US,AUS) 8% (EC) 3% (JP) |
EC,USA, AUS, JP |
Genotoxic in bacteria[54] |
| Cinoxate |
2-Ethoxyethyl p-methoxycinnamate |
3% (US) 6% (AUS) |
USA, AUS |
Not tested |
| Dioxybenzone |
Benzophenone-8 |
3% |
USA, AUS |
Not tested |
| Oxybenzone |
Benzophenone-3, Eusolex 4360, Escalol 567 |
6% (US) 10% (AUS,EU) 5% (JP) |
EC, USA, AUS, JP |
Not tested |
| Homosalate |
Homomethyl salicylate, HMS |
10% (EC, JP) 15% (US,AUS) |
EC, USA, AUS, JP |
Not tested |
| Menthyl anthranilate |
Meradimate |
5% |
USA, AUS |
Not tested |
| Octocrylene |
Eusolex OCR, 2-cyano-3,3diphenyl acrylic acid, 2-ethylhexylester |
10% |
EC,USA, AUS, JP |
Increases ROS[7] |
| Octyl methoxycinnamate |
Octinoxate, EMC, OMC, Ethylmethoxycinnamate, Escalol 557, 2-ethylhexyl-paramethoxycinnamate, Parsol MCX |
7.5% (US) 10% (EC,AUS)20% (JP) |
EC,USA, AUS, JP |
|
| Octyl salicylate |
Octisalate, 2-Ethylhexyl salicylate, Escalol 587, |
5% (EC,USA,AUS) 10% (JP) |
EC,USA, AUS, JP |
Not tested |
| Sulisobenzone |
2-Hydroxy-4-Methoxybenzophenone-5-sulfonic acid,
3-benzoyl-4-hydroxy-6-methoxybenzenesulfonic acid, Benzophenone-4, Escalol 577
|
5% (EC) 10% (US, AUS, JP) |
EC,USA, AUS, JP |
|
| Trolamine salicylate |
Triethanolamine salicylate |
12% |
USA, AUS |
Not tested |
| Avobenzone |
1-(4-methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione, Butyl methoxy dibenzoylmethane, BMDBM, Parsol 1789, Eusolex 9020 |
3% (US) 5% (EC,AUS)10% (JP) |
EC, USA, AUS, JP |
Not available[55] |
| Ecamsule |
Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid |
10% |
EC, USA, AUS |
Protects against skin tumors in mice[56][57][58] |
| Titanium dioxide |
CI77891 |
25% (No limit Japan) |
EC,USA, AUS, JP |
Not tested |
| Zinc oxide |
|
25% (US) 20% (AUS)
(EC-25% provided particle size >100 nm) (Japan, No Limit)
|
EC,USA, AUS, JP |
Protects against skin tumors in mice[56] |
Other ingredients approved within the EU[59] and other parts of the world,[60] which have not been included in the current FDA Monograph:
| UV-filter |
Other names |
Maximum concentration |
Permitted in |
| 4-Methylbenzylidene camphor |
Enzacamene, Parsol 5000, Eusolex 6300, MBC |
4% |
EC, AUS |
| Tinosorb M |
Bisoctrizole, Methylene Bis-Benzotriazolyl Tetramethylbutylphenol, MBBT |
10% |
EC, AUS, JP |
| Tinosorb S |
Bis-ethylhexyloxyphenol methoxyphenol triazine, Bemotrizinol, BEMT, anisotriazine |
10% (EC, AUS) 3% (JP) |
EC, AUS, JP |
| Neo Heliopan AP |
Bisdisulizole Disodium, Disodium phenyl dibenzimidazole tetrasulfonate, bisimidazylate, DPDT |
10% |
EC, AUS |
| Mexoryl XL |
Drometrizole Trisiloxane |
15% |
EC, AUS |
| Benzophenone-9 |
Uvinul DS 49, CAS 3121-60-6, Sodium Dihydroxy Dimethoxy Disulfobenzophenone [61] |
10% |
JP |
| Uvinul T 150 |
Octyl triazone, ethylhexyl triazone, ET |
5% (EC, AUS) 3% (JP) |
EC, AUS |
| Uvinul A Plus |
Diethylamino Hydroxybenzoyl Hexyl Benzoate |
10% (EC,JP) |
EC , JP |
| Uvasorb HEB |
Iscotrizinol, Diethylhexyl butamido triazone, DBT |
10% (EC) 5% (JP) |
EC, JP |
| Parsol SLX |
Dimethico-diethylbenzalmalonate, Polysilicone-15 |
10% |
EC, AUS, JP |
| Isopentenyl-4-methoxycinnamate |
Isoamyl p-Methoxycinnamate, IMC, Neo Heliopan E1000, Amiloxate |
10% |
EC, AUS |
Many of the ingredients not approved by the FDA are relatively new and developed to absorb UVA.[62]
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External links
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Sunscreening agents approved by the US FDA or other agencies |
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| UVA: 400–315 nm • UVB: 315–290 nm • chemical agents unless otherwise noted |
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| UVA filters |
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| UVB filters |
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| UVA+UVB filters |
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