Agents Affecting Pigmentation
Agents Affecting Pigmentation
Agents Affecting Pigmentation
group of normal people. The ratio of the minimal erythema dose with sunscreen to the minimal erythema dose
without sunscreen is the SPF. Fair-skinned individuals who sunburn easily are advised to use a product with an SPF
of 15 or greater.
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SUNSCREENS
Introduction
Photoprotection from the acute and chronic effects of sun exposure is readily available with sunscreens. The major
active ingredients of available sunscreens include chemical agents that absorb incident solar radiation in the UVB
and/or UVA ranges and physical agents that contain particulate materials that can block or reflect incident energy
and reduce its transmission to the skin. Many of the sunscreens available are mixtures of organic chemical
absorbers and particulate physical substances. Ideal sunscreens provide a broad spectrum of protection and are
formulations that are photostable and remain intact for sustained periods on the skin. They also should be
nonirritating, invisible, and nonstaining to clothing. No single sunscreen ingredient possesses all these desirable
properties, but many are quite effective nonetheless.
UVA Sunscreen Agents
Currently available UVA filters in the United States include (1) avobenzone, also known as Parsol 1789; (2)
oxybenzone (2-hydroxy-4-methoxy-benzophenone); (3) titanium dioxide; and (4) zinc oxide. Additional UVA
sunscreens, including ecamsule (MEXORYLSX and XL), bisethylhexyloxyphenol methoxyphenyl triazine
(TINOSORBS), and methylene bisbenzotriazolyl tetramethylbutylphenol (TINSORB M), are available in Europe
and elsewhere but not in the United States.
UVB Sunscreen Agents
There are numerous UVB filters, including (1) PABA esters (e.g., padimate O); (2) cinnamates (octinoxate); (3)
octocrylene (2-ethylhexyl-2-cyano-3,3 diphenylacrylate); and (4) salicylates (octisalate).
The major measurement of sunscreen photoprotection is the sun protection factor (SPF), which defines a ratio of
the minimal dose of incident sunlight that will produce erythema or redness (sunburn) on skin with the sunscreen in
place (protected) and the dose that evokes the same reaction on skin without the sunscreen (unprotected). The SPF
provides valuable information regarding UVB protection but is useless in documenting UVA efficacy because no
standard systems have been developed to measure UVA protection. Such protocols are needed because more than
85% of solar ultraviolet radiation reaching earth's surface is UVA, which penetrates more deeply into human skin
than does UVB and appears to play an important role in photoaging and photocarcinogenesis. Despite their
universal availability, a major problem with sunscreens is the fact that people do not use them on a regular basis. In
a population study evaluating the use of sunscreens in northern England, it was reported that only 35% of females
and 8% of males regularly used sunscreens (Ling et al., 2003). Furthermore, 22% of those surveyed used no
sunscreen at all, and 34% recalled at least one sunburn reaction in the previous 2 years.
There is evidence that the regular use of sunscreens can reduce the risk of actinic keratoses (Thompson et al.,
1993) and squamous cell carcinomas (SCCs) of the skin. One study noted a 46% decrease in the incidence of SCCs
in people who used sunscreen regularly for 4.5 years (Green et al., 1999).
Except for total sun avoidance, sunscreens are the best single method of protection from UV-induced damage to the
skin. There is a need for more definitive answers to questions related to the efficacy of sunscreens in reducing skin
cancer risk. Prospects for more effective photoprotection are excellent as better sunscreen components are
developed and as more careful evaluations are performed (Rigel, 2002).