The proper way to use sunscreen

Created date

March 2nd, 2016
sunscreen products
sunscreen products

Although a little color might make you appear robust, there is really no such thing as a “healthy” suntan. Rather, a lifetime of sun exposure can result in skin cancer, the most common type of cancer in the United States, according to the National Institutes of Health.  

Types of ultraviolet radiation

The three types of ultraviolet (UV) radiation coming from the sun are UVA, UVB, and UVC. They differ according to relative wavelength and the type of damage they cause. UVA has the longest wavelength and can thus penetrate deep skin layers. “It was once thought that UVA wasn’t responsible for skin cancer, but research shows that UVA from sunlight is in fact the main cause of skin cancer,” says Charles E. Crutchfield, III, M.D., clinical professor of dermatology at University of Minnesota Medical School in St. Paul, Minn. 

“UVB is mainly responsible for sunburns, but is considered generally safe with respect to skin cancer,” Crutchfield adds. Both UVA and UVB cause skin to age. UVC has the shortest wavelength and is almost entirely absorbed by the Earth’s ozone layer. 

How sunscreen works

You practically need a degree in chemistry to interpret the components on a label of sunscreen. 

The main categories of ingredients are minerals, such as titanium and zinc, and chemical compounds such as avobenzone. You might see more than one chemical compound suffix on labels. Others besides -benzone include –salate, -oxate, and -crylene. “Mineral-based and chemical-based sunscreens work differently,” Crutchfield says. “Minerals provide a physical block and chemicals absorb and break down UV radiation.” 

Recent FDA rules

In 2011, the Food and Drug Administration (FDA) issued standards to eliminate false claims by manufacturers. For example, sunscreens can be advertised as water- (or sweat-) resistant, not waterproof or sweatproof.

Sun protection factor (SPF) can be confusing. SPF is the amount of protection your skin receives. For instance, if you typically burn in 10 minutes without sunscreen, an SPF 30 theoretically means you can stay in the sun 30 times longer, or 300 minutes, without burning. But SPF does not take into account the rate that the product wears off. “True SPF can vary depending on the person, the weather, or the amount of activity,” says Ramzi W. Saad, M.D., board-certified dermatologist at South Shore Skin Center in Boston, Mass. 

SPF numbers are assigned based on how much UV they block. SPF 15 blocks 93%, SPF 30 blocks 97%, and SPF 50 blocks 98%. Higher numbers do not confer significantly more protection, according to the Skin Cancer Foundation.

“The most effective sunscreens have the term ‘broad spectrum’ on the label, which means that they screen out UVB and UVA rays,” Saad explains.

Proper use

Studies show that most people use about one-fourth to one-half the amount of sunscreen they should. The Skin Cancer Foundation and the American Academy of Dermatology both recommend using at least one ounce to cover your body. To visualize that amount, think two tablespoons, a golf ball, or the amount in a 1-ounce shot glass. A dollop the size of a nickel should adequately cover your face. 

Many sources indicate you should choose at least SPF 15; anything less has not been shown to prevent skin cancer. “I recommend using at least SPF 30,” Saad says. “Older adults are more likely to burn, so they need an effective product.”  

Keep your watch handy when using sunscreen. Slather it on 15 to 30 minutes before going outside in order to allow the ingredients to adequately bind to your skin. “Pay attention to when you first put it on,” Saad says. “Reapply it every two hours, even if the product is water-resistant. If you are swimming, sweating, or very active, reapply it more often.”

UV radiation reaches your skin all year, so experts recommend applying sunscreen every day to exposed parts of your skin.

Sunscreen substitutes

Some people who are sensitive to the active ingredients of sunscreen need to cover up with clothes. “Look for clothing with a tight weave,” Crutchfield says. “Some manufacturers make clothing specifically designed to screen UV radiation.”

Sun-protective clothing can carry an ultraviolet protection factor (UPF) label. Unlike SPF, UPF indicates what fraction of radiation reaches your skin. For example, a UPF 50 allows in 1/50th UVA and UVB.

According to the National Cancer Institute, the majority of common skin cancers occur on skin regularly exposed to sunlight, such as the head, face, and neck. Thus, hats should have wide brims that extend far enough to shield your entire head and neck. 

Whether you choose mineral-based, chemical-based, or combination sunscreen, finding the ideal sunscreen for you may involve some trial and error. “Everyone’s skin is different,” Crutchfield says. “Nevertheless, I tell my patients that the sunscreen that works best is the sunscreen used.”


When does sunscreen expire?

Most sunscreens are designed to retain their original strength for three years. But experts say that if you are using it correctly, you will use up the bottle long before that.