Sunscreening Agents (Molecule of the Month for August 2002)
Sun block is an important part of summer fun. But how does it work? Sun block can work in two ways, physically and chemically. A sun block is simply a barrier between the skin and the sun, it can be either physical, chemical or both. Sunscreens are made up of chemicals that can absorb specific wavelengths of the sun's spectrum. Physical protectors, such as zinc oxide, reflect UVA rays, whereas most chemical protectors absorb UVB rays. There are a few chemical agents that absorb UVA rays, such as Parsol 1789; however, it is impossible to block out all of the UVA rays using sun block. Octyl methoxycinnamate Parsol 1789 Octisalate Titanium dioxide Octicrylene
Compounds with high molar absorptivity in the UVA/UVB range can be used as sun blocks. There are many compounds that have this characteristic, however many of them are harmful for human skin, such as PABA, a sunscreen agent that isn't used anymore because of widespread allergic reactions to the chemical. Therefore, compounds that are stable, hypoallergenic, and sometimes waterproof are needed to be successful sun screening agents.
2-hydroxy-4-methoxy-benzophenone - Also known as oxybenzone, of the benzophenone group of chemicals, this compound absorbs the full UVA and UVB light spectrum, but is usually recognized as protection from UVA light.
Although we cannot see ultra violet light, it is part of the sun's spectrum, so we are exposed to it every day. Ultra violet is the component of light that causes keratosis (tanning), erythema (reddening), sunburn, and melanoma. This is because, as the wavelength of UV light is shorter than that of the visible spectrum, it has more energy and therefore can burn our skin.
Ultra violet light has been categorized into three main sections. The wavelength of ultra violet light is shorter than that of the visible spectrum, and UVC is the shortest, and also the most dangerous of the three. UVC's wavelength is from 100nm to 290nm, and lucky for us, the ozone keeps all UVC light off of the surface of the Earth. UVB light, responsible for sunburn, has a wavelength from 290nm to 320nm. Scientists have not yet determined the full effects of UVA light on our health, but it is under suspicion as a potential cancer-causing agent. It takes hundreds of thousands of times more UVA light than UVB light to achieve the equivalent skin damage. UVA light has a wavelength from 320nm to 400nm.
Formal Chemical Name (IUPAC)
Update by Siobhán McPherson
(Molecule of the Month for August 2002 )
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