Science Behind the Use of Sunscreen

Summer is not over yet. In fact, the way the weather has been acting up, we may end up with many more days of sunshine. May be we will get an early winter. But as long as the sun is shining, it continues to emit the harmful ultraviolet (UVR) rays. So, do not be in a hurry to put away your sunscreen lotion.

Chemical sunscreens were discovered in 1926. By 1928, the first commercial sunscreen, containing benzyl salicylate and benzyl cinnamate was marketed in the United States. Subsequent sunscreen evolution was primarily directed toward ultraviolet B (UVB) protection to lessen development of sunburn from overexposure to the sun.

Since 1960, the sunscreens contain para-amino-benzoic acid (PABA). It wasn’t until 1980, that sun protection factor (SPF) 15 became available in the market. PABA has several disadvantages and it has been replaced by PABA esters. These absorb well in the UVB range, are easier to formulate in nonalcoholic vehicles, and are less staining and less allergenic. Researchers continue to develop better sunscreens. Some scientists have determined that the viscous “red sweat” of the hippopotamus is an excellent, broad spectrum sunscreen. May be next time you see me, I will smell like a hippo.

Sunscreen should be efficient, water resistant and safe. It should spread easily, maximize skin adherence, should be non-stinging, non-staining, and inexpensive. Most popular sunscreens are available in creams and lotions (emulsions). Both are oil-in-water or water-in-oil preparations, although lotions spread more easily. Some sunscreens are oil based and greasy, some are in gel form but they tend to sting and irritate the skin. Sunscreens in the form of a stick are wax based but are difficult to apply in larger areas. Aerosols are wasteful with spray lost to the air. Increasingly, sunscreens are being incorporated into cosmetics, including lipsticks, and moisturizers.

The ability of a sunscreen to protect the skin from UVR-induced erythema is measured by the SPF. Erythema is defined as redness of the skin caused by dilatation and congestion of the capillaries, often a sign of inflammation or infection. In this case, the redness is from sunburn.

SPF 15 blocks 93 per cent of UVB. Some argue that SPF 15 is sufficient and that higher labeling claims are misleading and costly for consumers. But some studies have shown that higher SPF (SPF 30) sunscreens conferred better clinical and microscopic tissue benefits.

Most people who use sunscreens apply it at much lower concentrations than the 2 mg/cm2 at which they are tested. The resultant SPF is considerably reduced, typically to about 20 to 50 per cent of the labeled SPF for chemical sunscreens. It is important to remember that under-application, uneven application and delayed application of sunscreens result in unnecessary sun exposure and skin damage.

What the sunscreen does is to lessen the development of sunburn from overexposure to the sun by absorbing UVB sunrays. Recurrent sunburn causes permanent damage to the skin and causes skin cancers like squamous cell cancer (SCC), basal cell cancer (BCC) and melanoma. But the use of sunscreen alone will not reduce the incidence of skin cancer, especially BCC and melanoma. You should avoid sunburn by other means wearing appropriate clothings, wide-brimmed hat and appropriate sunglasses and avoid sun exposure between 11 a.m. and 3 p.m.

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