How Does Sunscreen Work? Hot Answers to a Burning Question

July 2, 2025

African american woman smiling confident applying sunscreen lotion at seaside

You don’t have to run and hide as the summer sun beats down. Knowing how sunscreen works and wearing sunscreen can help you have fun in the sun without painful, dangerous burns.

“Gentle sun rays are important,” says Dr. Jack Levy, assistant attending dermatologist and assistant professor of Clinical Dermatology at Weill Cornell Medicine. “They help with vitamin D production, mood elevation and sleep regulation.”

Smart sun exposure, however, requires the right sunscreen.

Understanding How Sunscreen Works

While there are countless sunscreen brands, all sunscreens aim to protect you from the sun’s harmful ultraviolet (UV) rays. They do this in one of two ways.

Absorbing UV rays. Avobenzone and octisalate are common active ingredients in chemical sunscreens. These chemicals soak up UV rays, keeping them from damaging your skin.
Reflecting UV rays. Minerals, such as titanium dioxide or zinc oxide, act as a barrier. These are physical sunscreens that keep UV rays from penetrating your skin.

Hybrid sunscreens are also available and contain active ingredients from both types of sunscreen.

Reading Sunscreen Labels

Years ago, labels on sunscreen products only mentioned protection against UVB rays. That’s because UVB rays cause sunburns and many skin cancers. According to the American Cancer Society, UVA rays may also result in skin cancer, along with wrinkles and other sun damage.

What can you do to protect against UVA and UVB rays and maximize your summertime sun safety? Learning to read and understand sunscreen labels is a good place to start. Words you’ll find there include:

Baby. Sunscreens targeted at babies are less likely to cause skin irritation. Adults can choose sunscreen for sensitive skin, which helps prevent irritation.
Broad-spectrum sunscreen. These sunscreens protect against UVA and UVB rays.
SPF. Short for sun protection factor, SPF explains how much UVB a sunscreen protects you against. No sunscreen filters all UVB, but SPF 15 reduces sun exposure by 93 percent, SPF 30 by 97 percent and SPF 50 protects against about 98 percent of harmful UVB rays.
Water-resistant. These sunscreens last 40 minutes while you’re sweating or in water. Very water-resistant sunscreen can last twice as long.

Your Role in How Sunscreen Works

No matter what kind of sunscreen you choose, you must use it properly to protect your skin. To make the most of your sunscreen, do the following:

Apply sunscreen every day at least 30 minutes before going outside.
Cover all exposed skin with sunscreen.
Reapply at least every two hours and more often if you’re sweating or swimming.
Spend time in the shade.

Don’t like how a sunscreen smells or feels on your skin? Shop around for another option. There are plenty out there, and finding the right one for you can make the difference in keeping your skin healthy.

“The best sunscreen is the one you’ll use,” Dr. Levy says, “so try a few until you find the one that feels best on your skin.”

Want help monitoring your skin and keeping it as healthy as possible? Find a doctor at Weill Cornell Medicine today.