Whether the sky above is a bright blue or steely gray, the sun’s rays are raining down billions of photon particles per second on us. And, in addition to the warmth and light we crave, those kaleidoscopic rays contain ultraviolet (UV) radiation, the source of sunburn, premature skin aging and skin cancer, which more of us get than all other cancers combined.

If you plan to do the prudent thing and slather on sunscreen before your outdoor activity, then you have some choices to make. This article covers key considerations in selecting and applying sunscreen:

This article will cover:

Note: Clothing with UPF-rated fabric protects skin more effectively than any sunscreen. So your best strategy is to cover as much as possible with protective clothing and to save sunscreen for the remaining areas of exposed skin. Read Sun Protection Clothing: How to Choose for more details.

Understanding Sunscreen Ratings 

Sunscreen labels contain key info that helps you evaluate their effectiveness. All labels must list Sun Protection Factor (SPF), a number that reflects a sunscreen’s ability to protect skin from rays that cause sunburn. In addition, sunscreens that pass the relevant tests might list other protections: broad-spectrum coverage against rays that prematurely age skin, and water resistance for a specified amount of time.

What SPF Ratings Mean

SPF is a number that indicates how well a sunscreen shields unprotected skin from damage caused by a particular type of UV radiation: sunburn-causing, skin-cancer-promoting UVB rays. The scale isn’t simple and intuitive, though:

Keys to understanding SPF ratings. Keep in mind the following guidelines as you think about what SPF rating you want:

What “Broad Spectrum” Means

Ultraviolet (UV) radiation includes rays of varying wavelengths. In addition to the UVB rays noted above, you need protection from UVA rays, which prematurely age skin and also contribute to skin cancer. Rather than a numerical rating, UVA-ray protection is indicated by a specific term: broad spectrum.

Sunscreens labeled broad spectrum shield skin from both UVB and UVA rays. The FDA says that a broad spectrum’s UVA protection level will be roughly proportional to its UVB protection level (SPF rating).

Water and Sweat Resistance

“Water resistant” means the sunscreen is formulated to perform well despite the presence of water or sweat. Because no sunscreen lasts indefinitely when you’re swimming or sweating, the FDA bans the use of “waterproof” or “sweatproof” on product labels. They have a specific test, though, and you should find one of two ratings:

Be aware, though, that toweling off your skin removes sunscreen. So, regardless of the water resistance rating and time you think you should have left, you need to reapply sunscreen immediately after you use a towel.

Ingredient Considerations

The FDA regulates what ingredients are allowed in sunscreens. The list below highlights some of those key ingredients, including ones that FDA critics are wary about: 

Oxybenzone: Because this chemical has been implicated in harming coral-reef ecosystems worldwide, certain nations and the state of Hawaii have banned sunscreens containing this ingredient. Highly effective against UVB rays and widely used in sunscreens, oxybenzone has also caught the eye of health researchers, who have found trace amounts of it in blood samples of people throughout the U.S. Most countries, including the U.S., limit the percentage of oxybenzone in sunscreens.

Octinoxate: This chemical sunscreen ingredient is also banned in Hawaii because of concerns that it has negative effects on coral health.

(Note: Some sunscreens are labeled as “reef-safe” or “reef-friendly.” These terms do not have agreed upon definitions, and their use is not regulated by the FDA or managed by a standard-setting organization. Most commonly, these terms are used to identify sunscreens that do not contain oxybenzone and octinoxate. However, there are other sunscreen ingredients and various environmental factors also suspected of impacting coral health. Climate change and many other variables have been linked to the decline of coral reefs, so it is hard to parse out which factors are of greatest concern.)

Para Amino Benzoic Acid (PABA): Causes allergic and photosensitivity reactions in some people. Products that do not use it often state “PABA-free” on their labels.

Parabens: These are preservatives (e.g., methylparaben) found in some skin-care products including some sunscreens. Butylparaben has been implicated in coral reef bleaching, and some health questions surround parabens in general, so a growing number of brands omit them and promote their sunscreens as “paraben-free.”

Fragrances: Other than the fact that they’re not really needed, the concern here is that they can sting your eyes or trigger allergic reactions. So they’re good to avoid for kids, as well as adults who expect to swim or sweat.  

Nano particles: The ability to make these incredibly small particles is relatively new and their properties are not fully understood yet. They can pass easily through cell membranes, for example, which can be valuable for some purposes but concerning as well. No nano-particle risks have been found in sunscreens, but you might see sunscreens stating that they are “nano-free” or “non-nano.” There is no approved definition of these term by the FDA, but there are definitions approved in Europe and Australia, and some brands use those definitions to create their products.

Zinc oxide and titanium dioxide: Mineral sunscreen ingredients block UVA and UVB rays. Unlike sunscreens that rely on synthetic chemicals to block rays, products that contain these mineral ingredients sometimes market themselves as “natural” “organic” or “reef-safe.” Many sunscreens that contain these minerals use nano particles, in part, to provide a smoother, clearer application.

Learn more: For a more comprehensive look at ingredients of concern, you can check out information from organizations like the Environmental Working Group (EWG). It’s also worth reminding yourself, though, that the science behind skin-cancer risks and current sunscreens’ ability to reduce those risks is indisputable.

Application Guidelines

Almost everyone uses too little and almost no one puts it on correctly. Embrace the application tips below and you’ll be one of the few who uses sunscreen the right way:

Sunscreen and infants: Use only shade to protect kids under 6 months of age because their skin can easily absorb sunscreen.

Spray sunscreens: The FDA recommends against using sprays on kids because of the likelihood of inhalation and respiratory problems like asthma. In addition, sprays encourage the application of too little sunscreen. Sprays can be handy for applying over thinning hair, though a hat is still your best bet there.

Sunscreen expiration dates: A rule of thumb is that a sunscreen is good for up to three years, though the best indicator is the “use by” date on a product. Whenever possible, store sunscreen in a cool dry place because heat and humidity hasten its demise.

Total UV Protection

Conscientious UV protection requires a multifaceted approach:

Factors that call for extra vigilance in reducing your UV exposure, including proper use of sunscreen. Risks from exposure to UV rays greatly increase when any of the following factors come into play:

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