SciTech

How Things Work: Sunscreen

Credit: Photo illustration courtesy of Joe Shlabotnik via flickr Credit: Photo illustration courtesy of Joe Shlabotnik via flickr

Whether it was a day at the beach, working in the yard, or being lazy by the pool, your skin had been subjected to the damaging effects of the sun’s ultraviolet (UV) rays. Your result — either a painful burn or a healthy glow — probably depended on the use of (or lack of) one indispensable item: sunscreen.

As its name suggests, sunscreen protects you from the sun’s harmful UV rays — rays whose wavelengths are shorter than those of visible light. And while most of the sun’s rays are UV, our atmosphere and ozone layer are able to filter out much of this damaging radiation.

The UV light that gets by, however, is harmful to the DNA in our skin; it results in a tan (yes, tans are signs of damage), burns, or even skin cancer with chronic exposure. The three types of UV radiation are UV-A, UV-B, and UV-C, from longest to shortest wavelength, respectively. Of the three, UV-B rays are the ones that cause sunburn, while UV-A can cause damage within the skin, contributing to skin cancer.

If the sun leaves you with a nasty burn, it’s a sign that the UV-B rays have damaged your skin cells. According to Discovery Health, skin cells that are the most susceptible to burn are those without any sort of melatonin — typically found in Caucasians without any sort of tan. When these cells get damaged, the body increases blood flow to the dermis, the second layer of skin, to bring in new cells that will repair the damage.

Sunscreen protects the skin from this invisible light through its unique chemical composition of inorganic and organic materials. The inorganic particles, such as titanium dioxide and zinc oxide, act as a sort of UV armor. The small particles sit on the skin and reflect the wavelengths of UV-B light. But many old sunscreens, since they depend primarily on inorganic materials, were thick and greasy.

Companies combat this issue with lighter, synthetic organic components that work by absorbing the UV light and then releasing the stored energy. According to a study by the University of Athens Medical School in Greece, these particles, such as octyl methoxycinnamate, gain energy when exposed to the UV rays and then release the energy through either heat release or isomerization — when a molecule rearranges its atoms. Additionally, many of the newer sunscreens have tiny inorganic particles of about 45 nanometers in size. For comparison, a sheet of paper is roughly 100,000 nanometers thick.

The SPF on sunscreens, or “Sun Protection Factor,” is meant to give an estimate for the rate of UV-B absorption, as well as the duration of how long the sunscreen is effective. To determine the effective duration of sun protection, simply multiply the SPF by 10. For example, SPF 10 will grant roughly 100 minutes of protection.

However, in terms of UV-B absorption, there is a ceiling to the SPF: With SPF 45 protecting from 98 percent of the sun’s UV-B rays, anything greater is “just silly,” James Spenser, the spokesman for the American Academy of Dermatology, told WebMD.

For optimal skin safety, use the entire recommended dose of sunscreen. It might seem that sunscreen manufacturers just want people to use more of their product, but in a recent article published in International Journal of Pharmaceuticals, researchers found that using less than the standard amount of sunscreen will increase the chances of getting burned.

It’s also important to remember that people can get burned during any season. Plenty of UV rays reach the ground any season of the year — not just summer. So whenever you’re planning on doing any activities out in the sun, remember to apply your inorganic and organic particles liberally. You’ll save your skin, and possibly your life.