Sunscreen
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Sunscreen or sunblock is a lotion that is applied to reduce skin damage by blocking ultraviolet radiation from the sun. The best sunscreens block both UV-B rays, which can cause sunburn, and UV-A rays, which cause invisible damage. Most sunscreens work by containing either an organic chemical compounds that absorbs ultraviolet light (such as oxybenzone) or an opaque materials that reflects light (such as zinc oxide), or both.
Most people apply sunscreen when participating in outdoor activities during the summer. However, some experts suggest wearing sunscreen on a daily basis to prevent cumulative damage, and to lower the risk of skin cancer. It is recommended that sunscreen be applied 30 minutes before exposure to the sun.
Sunscreen blocks the production of Vitamin D.
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History
The ancient Greeks used olive oil as a type of sunscreen. However, this was not very effective. Throughout the early twentieth century, H.A. Milton Blake, a South Australian chemist, as well as several other inventors attempted to create an effective sunscreen but failed.
It was not until 1944 that the first effective sunscreen was invented. At that time, World War II was in full swing and many soldiers were getting serious sunburn. A pharmacist called Benjamin Greene decided to create something that would save the soldiers from the sun’s harmful rays. In his wife’s oven, he created a sticky, red substance which he called "red vet pet". Greene tested it on his own bald head. It didn’t work nearly as well as modern sunscreens, but it was a start.
Greene then created a more user friendly sunscreen which he began selling to customers in and around Miami. He founded the Coppertone company and his sales boomed. The little protection his product offered had customers enthusiatic. People were no longer afraid of getting sunburn. In their eyes, the sun's harmful rays were conquered.
Sunscreen has come a long way since its initial conception. Modern products have much higher protection factors than Greene's sunscreen, and modern products can also be water- and sweat proof. But there are also negative effects. A lot of people rely too much on the product not understanding the limitations of the sun protection factor, assuming buying anything over 30 will automatically prevent them getting burnt no matter how long they can stay in the sun without protection. Too much sunbathing is one of the major causes of skin cancer across the world.
Sun protection factor
The SPF (sun protection factor) of a sunscreen is a laboratory measure of its effectiveness. The higher the SPF, the more protection a sunscreen offers against the Ultraviolet type B radiation that causes sunburn, the formula used to calculate an SPF is available here (http://www.arpansa.gov.au/uvrg/rginfo_p7.html). For example SPF 15 means that a user can nominally remain in the sun 15 times longer than would otherwise cause them to have sunburn. In real life the protection from a particular sunscreen depends on factors such as the:
- Skin type of the user
- Amount applied and if it is reapplied every 2 hours, while in the sun
- Time of day and season
- Percentage of UV reflected or scattered by the environment e.g. snow or sand.
- Amount of sunscreen the skin has absorbed.
The SPF is not a linear measure of the amount of Ultraviolet blocked. A sunscreen rated 15 blocks 93.3% of UV, and an SPF 30 sunscreen blocks 96.7%, according (http://www.arpansa.gov.au/uvrg/rginfo_p7.html) to the Australian Radiation Protection and Nuclear Safety Agency (http://www.arpansa.gov.au/index.htm). This is calculated as 14/15 = 93.3 or 29/30 = 96.7. In the first example, the sunscreen blocked 14 doses and the 15th produced an erythemal response in the skin. A 30+ SPF rated sunscreen will protect against sunburn but that does not mean it can be applied 30 times less often, or that users can stay out in the sun for 30 times longer without skin damage. Instead of linear, the graph is in the form (n-1)/n. Looking at this graph, anything over 15 (93.3%) is considered effective "enough" as it blocks most of the rays with little benefit in going over.
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. Normal sunscreen does not block UVA as effectively as UVB, and an SPF rating of 30+ may translate to significantly lower level of UVA protection according to a study from 2003 (http://www.raft.ac.uk/research/press_release_23_09_03.html/) by researchers funded by the RAFT trust (http://www.raft.ac.uk/). Some broad spectrum sunscreens do provide significant UVA protection. UVA also causes DNA damage to cells deep within the skin, according to a 2004 study (http://www.jidonline.org/cgi/content/abstract/122/5/1277) increasing the risk of malignant melanomas.
Due to consumer confusion over the real degree and duration of protection offered labeling restrictions are in force in several countries. In the United States in 1999 the FDA decided to institute the labelling of SPF 30+ for sunscreens offering more protection, and a similar restriction applies in Australia. This was done to discourage companies making unrealistic (http://www.fda.gov/bbs/topics/ANSWERS/ANS00955.html) claims about the level of protection offered e.g "all day protection", and because an SPF over 30 does not provide significantly better protection.
The following are the FDA allowable active ingredients in sunblocks:
- p-Aminobenzoic acid (PABA) up to 15 percent.
- Avobenzone up to 3 percent.
- Cinoxate up to 3 percent.
- Dioxybenzone up to 3 percent.
- Homosalate up to 15 percent.
- Menthyl anthranilate up to 5 percent.
- Octocrylene up to 10 percent.
- Octyl methoxycinnamate up to 7.5 percent.
- Octyl salicylate up to 5 percent.
- Oxybenzone up to 6 percent.
- Padimate O up to 8 percent.
- Phenylbenzimidazole sulfonic acid up to 4 percent.
- Sulisobenzone up to 10 percent.
- Titanium dioxide up to 25 percent.
- Trolamine salicylate up to 12 percent.
- Zinc oxide up to 25 percent.
Melanin
The hormone alpha-melanocyte stimulating hormone is made when the body is exposed to sunlight and is responsible for the development of the pigment melanin. Research is being done to create stable artificial forms of the hormone. A promising candidate, melanotan, might be useful in the prevention of skin cancer, by causing tanning without exposure to sunlight.
Usage
External links
- FDA monograph on sunscreen (http://vm.cfsan.fda.gov/~lrd/fr990521.html)