What are chemical sunscreens?

Dr. Ellen Marmur, MD

These are chemical ingredients that filter either UVB or UVA radiation. Instead of creating a physical block that deflects ultraviolet rays, they absorb the sun's light energy and convert it safely into thermal (heat) energy on top of the skin, which is then released. A primary scientific premise is that "energy is constant." It can be changed into different forms, like vapor changing to water, then changing to ice, but it's never really gone. So chemical sunscreens don't absorb the UV radiation as much as convert it into something benign (heat) that dissipates from the surface of your skin before it's able to reach the collagen in the dermis and the DNA in your cells. Chemical filters intercept that radiation and transform it into something much less dangerous.

The problem is that this photochemical reaction uses up sunscreen. Imagine that each chemical sunscreen molecule gets zapped and disappears the second it gets hit by a photon and converts to heat. Rather than wearing off, it is actually used up, like gasoline used by a car or food consumed by your body. That's why it must be reapplied. The more sun you are getting, the faster sunscreen is used up or breaks down.

Simple Skin Beauty: Every Woman's Guide to a Lifetime of Healthy, Gorgeous Skin

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Simple Skin Beauty: Every Woman's Guide to a Lifetime of Healthy, Gorgeous Skin

What if a leading dermatologist just happened to be your best friend and you could ask her anything? DR. ELLEN MARMUR, a world-renowned New York City dermatologist, answers all your questions with...

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.