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Everything You Need to Know About Sunscreen

After that long winter, we’re all ready for these warmer, sunnier days. Whether it’s on the beach, at a lake or in your own backyard, plans for soaking up some rays should include sunscreen.

Turns out there’s more to the white goop than you think—ingredients, SPF ratings and application instructions matter when picking out your protection. We took our questions about sunblock to Megan Evans, MD, a fellow in the Department of Dermatology at the UNC School of Medicine. Here are her answers.

What are some common ingredients in sunscreen and how do they work?

Most sunscreens contain multiple active ingredients to protect against both kinds of harmful ultraviolet rays—UVA and UVB. Those ingredients fall into two main categories: physical blockers and chemical absorbers. The common physical blockers are titanium dioxide and zinc oxide. They create a physical barrier between the skin and UV rays. Examples of chemical absorbers include oxybenzone, avobenzone, homosalate, and octinoxate. These absorbers do just that—absorb UV rays so that our skin doesn’t absorb them. Aside from the active ingredients, sunscreens contain many additional inactive ingredients. These may vary based on the brand and type of sunscreen, as in baby vs. sport, and may include antioxidants, vitamins, such as vitamin E, preservatives, fragrances and emollients.

What’s the difference between UVA and UVB rays?

UVA and UVB rays are both types of ultraviolet rays from the sun that reach the earth’s surface. While UVB rays do not penetrate quite as deeply as UVA rays, they cause sunburn and also play the biggest role in causing skin cancer. UVA rays also contribute to the formation of skin cancer, but their penetration into the deeper portions of the skin also leads to premature aging and wrinkling of the skin. UVA rays make up 95 percent of the UV rays that reach the earth’s surface.

What do different SPF ratings mean?

The SPF (sun protection factor) listed for a particular sunscreen reflects the degree of protection against UVB rays. Dermatologists generally recommend using a sunscreen with an SPF of at least 30, which correlates to protection against 97 percent of the sun’s UVB rays. Ultrahigh ratings of 100 or above actually aren’t that much more protective than an SPF 50, which blocks 98 percent of UVB rays. To make sure you’re using a sunscreen that offers sufficient protection against UVB and UVA rays, you should look for the term “broad-spectrum.”

How and when should I apply sunscreen?

Your first application of sunscreen should happen about 15 minutes before you go outside, and it should always be applied to dry skin. All areas of skin not covered by clothing should have sunscreen on them. Sunscreen should be reapplied every two hours, or more often if you’re swimming or sweating. To get the full protection of your sunscreen’s SPF, you need to apply it generously. Most people only apply about 25 to 50 percent of the recommended amount of sunscreen, which is one ounce (or one shot glass) of sunscreen with each application.

Do I need to pay attention to the expiration date?

Many, but not all, sunscreens have a listed expiration date. The FDA requires all sunscreens to maintain their protection for at least three years. If your sunscreen has either passed the listed expiration date or is over three years old, you should not use it. Also, do not use your sunscreen if the color or consistency has changed.

Are there chemicals or certain ingredients to avoid in my sunscreen?

I recommend avoiding sunscreens that also contain insect repellents, as sunscreen should be applied more often and more generously than insect repellent.

Should people with certain skin tones use more or less sunscreen?

It’s recommended that all people, regardless of skin color, use sunscreen. Skin cancer can develop even in people with darker skin types. Though some people are more prone to sunburns than others, sun damage occurs even in the absence of sunburn. That means even someone who never gets sunburned should still wear sunscreen.

Is sunscreen enough protection from the sun on its own?

No. Even the highest SPF sunscreens don’t protect against 100 percent of the sun’s harmful rays. In addition to sunscreen, I recommend sunglasses, wide-brimmed hats, protective clothing and seeking shade when possible. Also, keep in mind that sitting under a canopy doesn’t offer enough protection because the sun’s rays reflect easily off the sand and water.

Are there instances in which I should use sunscreen differently?

You may prefer to use a facial moisturizer containing SPF for the face, but make sure you follow the same application guidelines we discussed: SPF 30 or higher and reapply every two hours.  Also, many people often forget to protect their lips. Lip balms containing SPF are a good idea, as skin cancer can develop on the lips, too. Never use spray sunscreens on the face, as you should avoid inhaling the chemicals. Finally, you should avoid sunscreen on your infant’s skin until he or she is 6 months old. If your infant is younger than that and must be out in the sun, use protective clothing and shade to protect him or her.


Make an appointment with a physician at UNC Dermatology.