Sunscreen (also commonly known as sunblock, sun screen, sunburn cream, sun cream or block out and sometimes erroneously called suntan lotion) 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). Although sunscreen is sometimes called "indoor tanning lotion", the latter is different in that it is used to intensify UV rays whereas the former is used to block UV rays.
Medical organizations such as the American Cancer Society recommend the use of sunscreen because it aids in the prevention of developing squamous cell carcinomas and basal-cell carcinomas. Many sunscreens do not block UVA radiation, which does not cause sunburn but can increase the rate of melanoma, another kind of skin cancer, and photodermatitis, so people using sunscreens may be exposed to high UVA levels without realizing it. 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.
No medical association recommends not using sunblock.
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 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, while the second found that mothers with high levels of oxybenzone in their bodies were more likely to give birth to underweight baby girls.
Concerns have been raised regarding the use of nanoparticles in sunscreen. In 2006 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."
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 can decrease vitamin D synthesis. The significance of this is uncertain. 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.
The first effective sunscreen may have been developed by chemist Franz Greiter in 1946. 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. It has been estimated that Gletscher Crème had a sun protection factor of 2.
The first widely used sunscreen was produced by Benjamin Green, 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.
Sun protection factor (SPF) and labeling requirements 
The sun protection factor 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, as a multiple of the amount required without the sunscreen. There is a popular oversimplification of how SPF determines how long one can stay in the sun. For example, many users believe that, if they normally get sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun fifteen hours (i.e. fifteen times longer) without getting sunburn. This would be true if the intensity of UV radiation were the same for the whole fifteen hours as in the one hour, but this is not normally the case. Intensity of solar radiation varies considerably with time of day. During early morning and late afternoon, the sun's radiation intensity is highly diminished since it must pass through more of the Earth's atmosphere while it is near the horizon.
In practice, the protection from a particular sunscreen depends, besides on SPF, 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. 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. 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.
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) while Australia's upper limit is 30+. 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 (especially due to the logarithmic nature of the scale).
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. Numerous methods have been devised for evaluation of UVA and UVB protection. The most reliable spectrophotochemical methods eliminate the subjective nature of grading erythema.
Mathematically, the SPF 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 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'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. The implementation of this seal is in its phase-in period,[when?] so a sunscreen without it may already offer this protection.
A set of final U.S. FDA rules effective from summer 2012 defines the phrase "broad spectrum" as having a UVA SPF at least as high as the UVB SPF.
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 that 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 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 licence. 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, 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 Protection Grade of UVA (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. The FDA has considered banning such use because it can lead consumers to overestimate the effectiveness of products so labeled.
Sunscreens contain one or more of the following ingredients:
- Organic chemical compounds that absorb ultraviolet light.
- Inorganic particulates that reflect, scatter, and absorb UV light (such as titanium dioxide, zinc oxide, or a combination of both).
- 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. An example is Tinosorb M. Since the UV-attenuating efficacy depends strongly on particle size, the material is micronised to particle sizes below 200 nm. The mode of action of this photostable filter system is governed to about 90% by absorption and 10% by scattering of UV light.
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.
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% (EC- 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% (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|
|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-3,3-diphenyl acrylic acid, 2-ethylhexylester||10%||EC,USA, AUS, JP||Increases ROS|
|Octyl methoxycinnamate||Octinoxate, EMC, OMC, Ethylhexyl methoxycinnamate, 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|
phenyl)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|
|Ecamsule||Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid||10%||EC,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)||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|
|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 ||10%||JP|
|Uvinul T 150||Octyl triazone, ethylhexyl triazone, EHT||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.
* Time and Extent Application (TEA), Proposed Rule on FDA approval expected 2009
||This section contains instructions, advice, or how-to content. (October 2009)|
Excessive exposure to direct sunlight is potentially harmful. Excessive exposure can result in sunburn if a person does not wear sun protective clothing or use suitable sunscreen. Products with a higher SPF (Sun Protection Factor) level provide greater protection against ultraviolet radiation. However, in 1998, the Annual Meeting of the American Association for the Advancement of Science reported that some sunscreens advertising UVA and UVB protection do not provide adequate safety from UVA radiation and could give sun tanners a false sense of protection. A sunscreen should also be hypoallergenic and noncomedogenic so it does not cause a rash or clog the pores, which can cause acne.
For those choosing to tan, some dermatologists recommend the following preventative measures:
- Sunscreens that should block both UVA and UVB rays are called broad-spectrum sunscreens.
- Sunscreens need to be applied thickly enough to get the full SPF protection.
- Sunscreens should be applied 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after the sun exposure begins. Further reapplication is necessary only after activities such as swimming, sweating, and rubbing.
- Sun rays are strongest between 10 am and 4 pm. Sun rays are stronger at higher elevations (mountains) and latitudes near the equator.
- Wearing a hat with a brim and anti-UV sunglasses can provide almost 100% protection against ultraviolet radiation's entering the eyes.
- Reflective surfaces like snow and water can greatly increase the amount of UV radiation to which the skin is exposed.
Recent evidence indicates that caffeine and caffeine sodium benzoate increase UVB-induced apoptosis both in topical and oral applications. In mice, UVB-induced hyperplasia was greatly reduced with administration of these substances. Although studies in humans remain untested, caffeine and caffeine sodium benzoate may be novel inhibitors of skin cancer.
The dose used in FDA sunscreen testing is 2.2 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. Larger individuals should scale these quantities accordingly.
Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, research has shown 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 two 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. Some studies have shown that people commonly apply only 1/2 to 1/4 of the amount recommended to achieve the rated sun protection factor (SPF), and in consequence the effective SPF should be downgraded to a square 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 the linearity than expected by theory.
Updated package labeling standards in the United States have been under development since 1978.
A set of final FDA rules effective from summer 2012 bans "waterproof" claims, instead requiring claims of 40 or 80 minutes "water-resistant" protection. It also requires a standardized "Drug Facts" label and requires specific FDA approval for "sunblock" and "instant protection" labels. Claims of protection over two hours are not allowed without specific approval.
However, the compliance dates for these new sunscreen labeling requirements, published in June 2011, have been delayed by 6 months. The new implementation date for products with annual sales less than US $25,000 is December 17, 2013 and that for all other products is December 17, 2012.
Due to requests by several trade associations and the personal care industry, the FDA ultimately decided to extend the implementation period for 6 months from the original compliance date. This decision allows manufacturers adequate time for thorough testing and the full implementation of the new labeling requirements which cover:
- Broad Spectrum designation
- Use claims
- "Waterproof," "sweatproof" or "sunblock" claims
- Water resistance claims
- Drug facts
- Maximum SPF value on sunscreen labels to "50 +"
These changes shall enable consumers to identify and select suitable sunscreen products offering protection from sunburn, early skin aging and skin cancer.
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.
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- Labeling and Effectiveness Testing; Sunscreen Drug Products for Over-the-Counter Human Use; Delay of Compliance Dates Retrieved 09/27/2012
- US FDA Delays Implementation Deadlines for Sunscreen Labeling Requirements SGS SafeGuard Bulletin, Retrieved 09/27/2012
- FDA rulemaking history for sunscreens
- Make sure your sunscreen has The Skin Cancer Foundation's Seal of Recommendation
- Environmental Working Group: July 2009 Sunscreen Safety Guide and Report
- Information on what sunscreens are and how they work from The Skin Cancer Foundation
- 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)
- How does sunscreen work? Simple explanation from physics.org