Among the ancient cultures where lighter skin was more desirable, the purpose of sunscreen was solely cosmetic. Egyptians used rice bran, jasmine and lupine. Greeks used olive oil, and sandalwood was used in Ayurveda. Although the hazardous effects of sun exposure was little known then, it was later discovered that rice bran absorbs UV radiations, jasmine repairs DNA, and sandalwood and olive oil have several beneficial effects on skin. Serendipitously, usage of extracts and their concoctions by the ancient civilizations for cosmetic purposes helped them to ward off the harmful effects of sun exposure.
Sun emits harmful UV rays year-round. Even on cloudy days, up to 80% of the sun’s harmful UV rays can penetrate the skin. Snow, sand, and water increase the need for sunscreen because they reflect the sun’s rays. Radiations of sun mainly consist of UVA and UVB. While acute UVB exposure is responsible for erythema and sunburn, and UVA exposure is responsible for photo-aging (prematurely aging your skin, causing wrinkles and age spots), both UVA and UVB are responsible for suppression of immunity, and skin carcinogenesis in the long term. Earlier sunscreens filtered mostly the high-energy UVB wavelengths (290-320 nm), but more recent broad-spectrum products can effectively absorb the longer UVA wavelengths (320-400 nm) as well.
When sunscreen is applied uniformly to the skin at a thickness of 2 mg/cm2, its strength is determined by Sun Protection Factor, or SPF (weighted for UVB wavelengths). SPF is a ratio of the protected to unprotected minimal erythemal dose. While sunscreens of SPF-15 filter 93% UVB radiation, sunscreens of SPF-50 filter up to 98% of UVB radiation. Ingredients with broad-spectrum protection include benzophenones, cinnamates, sulisobenzone, salicylates, titanium dioxide, zinc oxide, avobenzone and ecamsule.
Apart from protection against the harmful radiations that could cause several cancers, sunscreens have also gained popularity in cosmetology and are used to prevent photo-aging. There are some safety concerns for the use of sunscreens such as photoactivation of sunscreen components, endocrine disruption, vitamin D deficiency, or increased risk of melanoma. However, these claims need to be supplanted with more corroborative evidence and a definitive causal association.
The following are some of the recommendations made by the American Academy of Dermatology for choosing and application of sunscreen:
-Use a broad-spectrum sunscreen with SPF 30 or higher and water resistant.
-Use enough sunscreen to generously coat all skin that will be not be covered by clothing. Follow the “1 ounce, enough to fill a shot glass” technique while applying, which is the amount needed to cover the exposed areas of the body. Protect your lips with a lip balm or lipstick that contains sunscreen with an SPF of 30 or higher.
-Apply sunscreen to dry skin 15 minutes before going outdoors.
-Reapply sunscreen approximately every two hours, or after swimming or sweating.