How Sunscreen works and more

Sunscreen (also known as sunblock, suntan lotion) is a lotion, spray or other topical product that helps protect the skin from the sun's ultraviolet (UV) radiation, and which reduces sunburn and other skin damage, ultimately leading to a lower risk of skin cancer.

Most sunscreens work by containing
1.an organic chemical compound that absorbs ultraviolet light (such as oxybenzone) or

2.an opaque material that reflects light (such as titanium dioxide, zinc oxide), or

3.a combination of both. Typically, absorptive materials are referred to as chemical blocks, whereas opaque materials are mineral or physical blocks.

The best sunscreens!-protect against both UVB (ultraviolet radiation with wavelength between 290 and 320 nanometres), which can cause sunburn, and UVA (between 320 and 400 nanometres), which damages the skin with more long-term effects, such as premature skin aging.

How much sunscreen is enough?
Dosing for sunscreen can be calculated using the formula for body surface area and subsequently subtracting the area covered by clothing that provides effective UV protection. The dose used in FDA sunscreen testing is 2 mg:/cm².

Example: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.

Is one application enough?
Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, 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.[2]
However, more recent research at the University of California 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 absorbed chemicals.

Note:Suntan lotion is an incorrect term for sunscreen as it is something entirely different. Suntan lotion is used to moisturize and maximize UV exposure and tanning, rather than block it. These are commonly called indoor tanning lotions when designed for use with tanning beds or just suntan lotion if designed for outdoor use and may or may not have SPF protection in them.

New and Improved!! In July 2006, the Food and Drug Administration (FDA) approved a new over-the-counter sunscreen that will be marketed in the United States as Anthelios SX. The new sunscreen offers better protection from UVA rays than do traditional broad-spectrum sunscreens, according to the manufacturer. This may help reduce the risk of various types of skin cancer — including melanoma and basal and squamous cell carcinomas. Better UVA protection also may reduce sun-related skin wrinkling. But the added protection may come at a cost. Although U.S. prices aren't yet available, similar products sold in Canada cost about twice as much as traditional sunscreens — or even more.