Ingredients
People rely on suntan lotion as a means to protect against the sun's harmful rays. Not only can the sun cause a sunburn as an immediate effect, it also can cause long-term effects in the form of skin wrinkling.
A suntan lotion begins with the combination of several ingredients, ranging from naturally occurring compounds (known as organic compounds) and those that are chemically created (known as inorganic compounds). Organic compound ingredients include octyl methoxycinnamate (listed as OMC on a label) and oxybenzone. Inorganic compound ingredients include zinc oxide and titanium oxide.
Application
Sunscreen should be applied roughly 30 minutes before a person goes into the sun to allow the sunscreen to adequately soak through the skin. A person should use a shot glass's worth of sunscreen to apply all over the body. The sunscreen should be applied well so as to avoid any being rubbed or sweated off before it has time to fully soak in.
When sunscreen is applied to the skin and the skin is then exposed to the sun, organic ingredients work to absorb ultraviolet radiation emitted by the sun. There are two types of ultraviolet radiation that broad-spectrum sunscreens protect against: ultraviolet A (UVA) and ultraviolet B (UVB). Wavelengths in UVA are the longest and penetrate the layers of skin underneath the epidermis--the outer layer of skin. Not all sunscreens protect against UVA rays, making purchasing a sunscreen labeled as "broad spectrum" of the utmost importance. Wavelengths in UVB are shorter than UVA and are the rays that cause sunburns.
When either UVA or UVB rays hit the skin with sunscreen on it, the organic compounds absorb the radiation, which is then given off as heat.
The inorganic compounds found in suntan lotion react slightly differently. Instead of emitting heat, inorganic ingredients scatter or reflect the ultraviolet radiation, meaning it bounces back toward the sun or toward another surface.
Sun Protection Factor
The final determinant in how suntan lotion protects the skin is the sun protection factor (SPF) assigned to the lotion. The SPF is a measure of UVB protection only. The SPF assignment measures the amount of rays the sunscreen filters out over time. For example, a suntan lotion with SPF 15 deflects 93 percent of the sun's rays, while one with SPF 30 deflects 97 percent of all rays. While many consider SPF a time-related measurement, it actually has nothing to do with time. Because the effectiveness of a suntan lotion's active ingredients reduce over time, a person should frequently reapply sunscreen--particularly if they have been sweating or swimming.
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