Sunscreens contain one or more UV filters of which there are three main types :
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. However, several epidemiological studies indicate an increased risk of malignant melanoma for the sunscreen user. 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.
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.
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. 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.
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.
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 study. 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.
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").. 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 vivomeasurements. . Numerous methods have been devised for evalaution 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
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.
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.
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.
|UV-filter||other names||maximum concentration||permitted in these countries||Results of safety testing|
|p-Aminobenzoic acid||PABA||15% (5% EC)||EC, USA, AUS||Protects against skin tumors in mice.|
|Padimate O||OD-PABA, octyldimethyl-PABA, σ-PABA||8%||EC, USA, AUS||not tested|
|Phenylbenzimidazole sulfonic acid||Ensulizole, Eusolex 232, PBSA, Parsol HS||4%(US,AUS) 8%(EC)||EC,USA, AUS||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)||EC, USA, AUS||not tested|
|Homosalate||Homomethyl salicylate, HMS||10%(EC) 15%(US,AUS)||EC, USA, AUS||not tested|
|Methyl anthranilate||Methyl-aminobenzoate, meradimate||5%||USA, AUS||not tested|
|Octocrylene||Eusolex OCR, 2-cyano-3,3diphenyl acrylic acid, 2-ethylhexylester||10%||EC,USA, AUS||Increases ROS|
|Octyl methoxycinnamate||Octinoxate, EMC, OMC, Ethylmethoxycinnamate, Escalol 557, 2-ethylhexyl-paramethoxycinnamate, Parsol MCX||7.5%(US) 10%(EC,AUS)||EC,USA, AUS||Protects against skin tumors in mice|
|Octyl salicylate||Octisalate, 2-Ethylhexyl salicylate, Escalol 587,||5%||EC,USA, AUS||not tested|
|Sulisobenzone||2-Hydroxy-4-Methoxybenzophenone-5-sulfonic acid, 3-benzoyl-4-hydroxy-6-methoxybenzenesulfonic acid, BENZ-4, Escalol 577||5%(EC) 10%(US, AUS)||EC,USA, AUS||Protects against skin tumors in mice|
|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)||EC, USA, AUS||Not available|
|Ecamsule||Mexoryl SX, Terephthalylidene Dicamphor Sulfonic Acid||10||EC, USA, AUS||Protects against skin tumors in mice|
|Titanium dioxide||25%||EC,USA, AUS||not tested|
|Zinc oxide||25%(US) 20%(AUS) (EC)Not listed as sunscreen, Still under SCCP review||EC,USA, AUS||Protects against skin tumors in mice|
Other ingredients approved within the EU and other parts of the world, which have not been tested:
|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|
|Tinosorb S||Bis-ethylhexyloxyphenol methoxyphenol triazine, Bemotrizinol, BEMT, anisotriazine||10%||EC, AUS|
|Neo Heliopan AP||Bisdisulizole Disodium, Disodium phenyl dibenzimidazole tetrasulfonate, bisimidazylate, DPDT||10%||EC, AUS|
|Mexoryl XL||Drometrizole Trisiloxane||15%||EC, AUS|
|Uvinul T 150||Octyl triazone, ethylhexyl triazone, ET||5%||EC, AUS|
|Uvinul A Plus||Diethylamino Hydroxybenzoyl Hexyl Benzoate||10% (EC)||EC|
|Uvasorb HEB||Iscotrizinol, Diethylhexyl butamido triazone, DBT||10%||EC|
|Parsol SLX||Dimethico-diethylbenzalmalonate, Polysilicone-15||10%||EC, AUS|
|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.