Most everyone knows to protect their skin from direct sunlight in the summer. But do you know how sunscreen works and what’s actually in the stuff you’re lathering all over your skin?

The College Today asked Tim Barker, an assistant professor of organic chemistry at the College of Charleston, to break down some of the ingredients in sunscreen and to separate the science from the hype. Here’s what he had to say:

Q: What chemicals are used in most sunscreens, and how do they work to protect us from damaging rays and from getting sunburns?

A: Both inorganic and organic chemicals serve as active ingredients in sunscreens. The inorganic compounds, titanium dioxide and zinc oxide, work by reflecting the radiation. The organic chemicals, two examples include avobenzone and oxybenzone, absorb the UV radiation with their chemical bonds before it interacts with the skin.

Q: What are some of the other applications for these same chemicals?

A: Zinc oxide is used in many things, but the most common use is in the vulcanization natural rubber into the rubber found in tires and other materials. Zinc oxide also has antibacterial properties so it has many medicinal uses.

Most of the organic compounds used as active ingredients in sunscreen are also used for sun protection in hair products and cosmetics.

Q: What should someone look for in a sunscreen for maximum protection?

A: It is important to use a sunscreen with active ingredients that protect against UV-A and UV-B rays. Avobenzone (organic) and zinc oxide (inorganic) are the only two active ingredients approved by the FDA and currently in use that protect against UV-A rays. Some studies with avobenzone and other organic chemicals used as active ingredients have suggested that these compounds may be endocrine disruptors. Especially for young children, zinc oxide would be the better active ingredient.

Q: What about sunscreen substitutes? Can natural ingredients whipped up at home provide protection against the sun?

A: The best natural sun protection would be to wear a hat and long sleeves. I would be wary of “natural” sunscreen ingredients. All natural ingredients are still chemicals.

Q: As a chemistry professor who can read a sunscreen label and actually know what the listed chemicals are, what type of sunscreen do you use?

A: I look for sunscreen with both UVA and UVB protection. Typically it will be SPF50 and contain zinc oxide which protects against UVA and UVB light as well as several other active ingredients.

Q: The U.S. Food and Drug Administration is investigating the efficacy and safety of spray-on sunscreens. Why would aerosol sunscreens be of particular concern?

A: When being exposed to a chemical there are different risks associated with the type of exposure. When you use a lotion, absorption through the skin is the main route of exposure. The aerosol sunscreens introduce inhalation as a route of exposure that has not been as well studied as absorption through the skin. If you like aerosol sunscreen, just spray it on your hand to apply it to your face to avoid inhalation.

Q: Have you ever had a bad sunburn? What went wrong?

A: I have gotten a sunburn at the beach when I did not reapply sunscreen after spending a lot of time in the water. The terms “waterproof” and “water-resistant” are really just marketing ploys on sunscreen bottles. The FDA has cracked down on the use of waterproof on sunscreen containers and made companies qualify how long a sunscreen is water-resistant since then, but I found out the hard way.