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Understanding Your Sunscreen

Written By: Luyang Zhang

Have you been dreaming of a summertime vacation—a getaway to the beach, maybe, or a few lazy days at home with a book? Whatever your plans (or lack thereof), protecting your skin from harmful ultraviolet radiation is something to keep in mind.

Ultraviolet (UV) radiation persists throughout the year, including on cloudy days, so wearing sunscreen is always important. Radiation, which is energy emitted from the sun, is the strongest during the spring and summer months between 10 a.m. and 4 p.m. (in the Northern hemisphere), meaning your trip to the beach is going to be a critical time to think about skin protection!

There are three main types of UV radiation: ultraviolet A, ultraviolet B, and ultraviolet C. The ozone and atmosphere absorb the entirety of UVC and the majority of UVB rays, while UVA rays don’t get filtered significantly. In addition, UVA wavelengths are longer than UVB wavelengths, rendering them capable of penetrating deeper into the skin to cause greater long-term damage. UVB rays, on the other hand, contribute to burning concentrated on the outer layer of skin.

Poorly protected skin leaves you vulnerable to issues including premature aging, wrinkles, eye damage, and, in more severe cases, skin cancer. In fact, 90% of nonmelanoma skin cancers in the United States are associated with UV exposure.

How Sunscreen Works

The strength of commercial sunscreen is denoted by its SPF, or sun protection factor, which generally varies from 15 to 100. SPF indicates how much longer the sun will take to burn your skin after you've applied product—for example, bare skin will take 15 times longer to burn after an SPF 15 sunscreen is (correctly) applied.

The SPF appropriate for each person varies and can depend on skin tone and level of sun exposure. Paler skin, which tends to burn more easily, usually requires a higher SPF.

There are two main categories of sunscreens, differentiated by the way they protect consumers: physical and chemical.

Chemical sunscreens are composed of carbon-based ingredients that cause a chemical reaction when exposed to UV rays, turning radiation into heat that is released off the skin. By nature, these sunscreens are designed to protect against either UVA or UVB rays, and contain chemicals like avobenzone, octisalate, octinoxate, and oxybenzone (the latter of which has raised health concerns for its connection to Hirshsprung’s disease, which impairs the development of nerve cells in the large intestine). However, chemical sunscreens tend to hold up against sweat and water better, often making them the more convenient choice.

Physical (also known as mineral) sunscreen contains inorganic ingredients that sit on top of the skin and physically reflect UV rays, putting the “block” in “sunblock.” The main ingredients in these sunscreens, usually titanium dioxide or zinc oxide, can protect against both UVA and UVB rays. Unlike chemical sunscreens, which require time to absorb into the skin and become effective, physical sunscreens offer protection immediately upon application. Unfortunately, these ingredients can also leave a chalky white cast on the skin.

Environmental Consequences

Sunscreen can have profound negative effects on the environment. 6,000 tons of sunscreen worldwide washes from skin into water annually, and sunscreen chemicals can have profound effects on marine ecosystems.

In particular, the compound oxybenzone, which is often found in chemical sunscreens, can act as a genotoxin in coral, damaging the DNA in a way that lowers the temperature at which the corals bleach. It can also encourage the expulsion of the algae living in coral tissue that keeps it alive. A study suggests that coral bleaching can occur with concentrations of just 10 microliters per liter of oxybenzone.

Some chemicals can act as endocrine disruptors in other species of sea life, reducing the egg count in fish or causing male fish to develop female characteristics. Worse still, these effects can be passed from generation to generation in mammals through mother’s milk, creating the potential for sunscreen to prompt long-term and widespread damage.

Consumers looking for more environmentally conscious ways to protect their skin at the beach should purchase sunblocks that don’t contain the greatest offenders to reef health: oxybenzone and octinoxate. Using physical, mineral-based sunscreens is less dangerous for corals. Wearing UV proof clothing and swimwear is also a great way to reduce the amount of sunscreen required to keep skin protected.

There has been a rise in sunscreens marketed as “reef safe,” specifically manufactured with substitutes for chemicals like oxybenzone. Some of these substitutes include octocrylene, homosalate, and octisalate. However, the benefits of these alternatives have been called into question. Some studies suggest they have their own ways of impairing the development and photosynthesis of aquatic producers.

There’s no doubt there are ways to improve the safety of sunscreens—and hopefully, there'll be better options and healthier ecosystems to enjoy in the near future. Meanwhile, continuing to wear sunscreen will keep you safe during your days in the sunshine!

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