How Much SPF Do You Need in Your Sunscreen?

Prevent sunburns and reduce your risk of skin cancer by selecting a sunscreen with the right Sun Protection Factor (SPF).

What is SPF?

SPF refers to the sun protection factor, or how well a sunscreen blocks harmful UVB rays, which cause sunburn and play a role in skin cancer. The higher the SPF number in a sunscreen, the more protection it offers.

“Broad spectrum” sunscreens offer some protection from a second type of rays, the UVA rays, according to the Skin Cancer Foundation. These rays prematurely age your skin and cause wrinkles and age spots.

Are higher SPF sunscreens better?

According to the American Academy of Dermatology, sunscreen with a 30 SPF will block 97 percent of the sun’s harmful rays. If you burn easily, purchase sunscreen with 50 SPF or higher, which blocks 98 percent of UV rays. Unfortunately, there isn’t a sunscreen that will block out 100 percent of harmful UV rays.

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For children, the best protection is clothing and shade. Look for specific sunscreens for children that include zinc oxide or titanium dioxide. These products leave a white film on the skin that actually blocks the rays.

“Unfortunately, there is a lot of misinformation out there about the use of sunscreen, leading individuals to avoid its use or to flock to ‘natural’ or ‘herbal’ sunscreens that have not been tested by the FDA,” said Ashley Wysong, MD, MS, assistant professor of clinical dermatology at USC Dermatology of the Keck School of Medicine of USC and director of Mohs (a new surgical technique) and dermatologic surgery at Keck Medicine of USC. “This is very risky, and it’s important for individuals to be well-informed and to discuss these decisions with their dermatologist.”

In addition to wearing sunscreen, Dr. Wysong recommended seeking shade, wearing protective clothing or hats, and avoiding peak UV hours.

Sunscreen application: how much and how often?

Many people select the correct SPF but still get sunburned. There are two reasons: uneven application and failure to reapply. In fact, the American Academy of Dermatology estimates most people apply only 25-50 percent of the recommended amount of one ounce, or enough to fill a shot glass.

Part of your daily routine should be to apply sunscreen on exposed areas. When at the beach or during outdoor activities, reapply every two hours or more if you will be in the water or sweating.

Concerned about past skin exposure to the sun? The Department of Dermatology at Keck Medicine of USC is recognized nationally for providing the highest quality of dermatology care.

By Heidi Tyline King

Schedule an appointment with a dermatologist to learn more. If you are in the Los Angeles area, make an appointment by calling (800) USC-CARE (800-872-2273) or by visiting