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The Science of Sunscreen

Published on 14 September 2020

As the hottest of the summer months slowly begin to cool into fall, it is prime time to catch the last of the warm, sunny days of September. But year-round, the need for proper sun protection is important.

University of Health Sciences and Pharmacy in St. Louis faculty members Ehren Bucholtz, Ph.D., assistant dean of the School of Arts and Sciences and director of the Master of Science in Medicinal Chemistry program, and Abby Yancey, B.S. ’02, Pharm.D. ’03, FCCP, BCPS, professor of pharmacy practice, unpacked the science of sunscreen from a molecular perspective to its importance in mitigating the development of skin cancer.

How does sunscreen help protect you from sunburns?

There are two common types of sunscreens based on the chemistry of organic and inorganic compounds, and both work by preventing or decreasing harmful ultraviolet light that can do damage to your skin.

Avobenzone is an example of an organic molecule used in sunscreens that absorbs ultraviolet (UV) light rays. With its aromatic ring system and conjugated double bond structure, avobenzone has proven to be effective in absorbing light.

"Atoms in a molecule form bonds through the sharing of electrons in orbitals," Bucholtz explained. "The electrons in bonds can exist in high or low energy orbitals. According to this theory, electrons in a low energy orbital can move to a higher energy orbital by absorbing light energy. These electrons can return to the original orbital, but release some light energy as it returns to its original configuration.

"This process is valuable for making sunscreens. High energy UV light is absorbed by the molecule, but the released light has a lower amount of energy which then causes less damage to the skin. The extended conjugated double bond system of avobenzone is key in this process because it creates more energy steps for the light to be filtered through."

Another common sunscreen product is zinc oxide- the white stuff you see slathered on lifeguard's noses in movies and TV. This is an inorganic compound and interacts with light differently than organic sunscreens.

"Sunscreens with zinc oxide don’t absorb light as they don't have the same molecular structure as organic molecules," Bucholtz explained. "In this case, zinc oxide particles reflect and diffract the light so that it is no longer concentrated on one area. It is the light diffraction that protects the skin because it dissipates harmful light energy before reaching the skin."

Are DIY sunscreens effective?

The longterm effects on the body from synthetics in sunscreen has not been adequately studied, but the idea of synthetic sunscreen ingredients being absorbed into the skin and entering the bloodstream has created concern among some individuals, leading them to seek and create DIY sunscreen options.

"Right now, we do not have an effective DIY alternative when it comes to sunscreen," Bucholtz said. "Coco butter, which some have suggested as a DIY sunscreen, is mostly composed of oleic acid. Similar to avobenzone, it has double bonds, but they are not conjugated. Therefore, it cannot absorb the same wavelengths of UV light. Coco butter also does not have the same ability to diffract light as zinc oxide does, which means you get the full dose of the UV rays onto your skin without any protection."

How do sunburns increase your risk of developing skin cancer?

Sunburns are an inflammatory reaction when the outer most layer of skin is burned by UV rays, also known as UV radiation. However, it is not so much the burn itself that can lead to skin cancer, it is what the body does to repair the damage that can create complications over the years.

"When you get a sunburn, your body has to fix it," Yancey explained. "This means your body has to alter your DNA in an attempt to fix the damaged cells, but there are times when the body may not be able to fix itself.

"There also have been studies that show UV rays can alter some of our tumor suppressing genes, making it less likely for those injured cells to repair before progressing into cancer. It's not typically one sunburn that causes cancer, but over time, your cells have less of a chance to fully repair and instead start growing erratically or too quickly leading to skin cancer."

What should you look for when picking a sunscreen?

Navigating the jargon and flashy labels of sunscreen can be confusing and sometimes misleading, but with just a little bit of knowledge, picking the right sunscreen for your needs and lifestyle can be simple.

"There are two types of UV rays. UVA rays are the ones that cause wrinkles and premature aging," Yancey said. "UVB rays are more likely to cause cancer. To block both types of UV rays, you want to select a broad-spectrum product.

"When it comes to SPF, or the sun protection factor, the number signifies the protection that sunscreen will give against UV rays in an amount of time compared to no sun protection at all. For example, SPF 15 will prevent your skin from burning 15 times longer than if you weren’t wearing sunscreen. The higher the SPF the longer your skin is protected but only for an estimated amount of time. Our current understanding is that SPF 15 products block about 93% of UVB rays, while SPF 30 blocks about 97%. This means that any SPF greater than 30 does not provide much more of a benefit.

"Another thing to look for when picking a sunscreen is whether or not it is water-resistant, which then affects how often you will need to reapply — so the main things to look for are broad-spectrum, SPF and water resistance.

"If you are concerned about sunscreens absorbing into the skin, your best option is a mineral sunscreen like zinc oxide or titanium oxide. These sunscreens essentially coat the skin to reflect light like a mirror."

Whether you wear long sleeves to block the sun's rays, apply a broad-spectrum sunscreen to decrease exposure or slather your nose in white to reflect UV light, there is a science behind protecting your skin from the sun.

From undergraduate studies in chemistry, including the University’s Bachelor of Science in Pharmaceutical Chemistry, to the Master of Science in Medicinal Chemistry, students at University of Health Sciences and Pharmacy in St. Louis have enriching opportunities at their fingertips so they can dig deeper into the science of our everyday.

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