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Sunscreen is typically considered a must-have for outdoor activities like summer picnics, hikes, and trips to the beach. But some people may not realize that there’s more to sunscreen than simply grabbing a product from the drugstore shelf, lathering up and heading outside for the day.

There are several variables and questions to consider such as: are all sunscreens the same? How often does one need to wear sunscreen? When to reapply? Does a higher SPF equal more sun protection than a lower SPF? We’ll take a look at these questions and more below.

How Sunscreen Works (and Why Some Are More Effective Than Others)

The sun produces ultraviolet rays that can be harmful to skin. There are two different types of UV rays: UVB and UVA. The former can cause sunburns, but the latter penetrates deeper into the skin causing premature aging. Both types of rays can increase a person’s risk of skin cancer – and this is true for all skin types. Although darker skin contains more melanin, it is not immune to the sun’s harmful effects. 

According to the CDC, the active ingredients in sunscreen interact with the skin to either block, reflect or scatter sunlight. But not all sunscreens have the same ingredients, and many sunscreens only offer protection against UVB rays.

A product’s SPF—or sun protection factor—refers to how well it protects against sunburn-causing UVB rays. To ensure you’re getting UVA protection in addition to UVB, it’s important to check for certain ingredients. David Andrews, senior scientist for the Environmental Working Group (EWG), recommends sunscreens with 3% avobenzone or at least 15% zinc oxide to shield against both UVA and UVB rays. 

When to Wear Sunscreen

Many people assume sunscreen is only necessary in the summer, but experts say it’s best to wear it year-round, regardless of the weather.

“You should wear sunscreen every day because when you are outside, you are constantly being exposed to UV radiation,” said dermatologist Katie Manno. “UV radiation even penetrates through the clouds, so yes, you should even be putting on the cream on cloudy days.”

You can check the UV Index for your area on the Environmental Protection Agency’s website – all you need is your zip code. Also, many weather apps now list a UV index.

Sunscreen is important in the wintertime. UV rays can still reach our skin even when we don’t feel the warmth of the sun as strongly. In fact, the ozone layer that protects the earth from harmful radiation is actually at its thinnest in winter—so it’s critical to protect yourself even when it’s freezing out. 

Some doctors advise wearing sunscreen even if you don’t plan on spending time outdoors. While inside, many of us spend the majority of our time in front of screens whether for work or for leisure. But screens emit a type of light that can be harmful to skin. According to Barbara Sturm, physician and founder of a skincare brand, “flat-screen monitors, computers, mobile phones and tablets emit high energy visible light, or HEV, a blue light that’s also emitted by the sun.” While HEV isn’t linked to skin cancer, it’s been known to cause premature aging. 

Many moisturizers and makeup already include sun protection, usually SPF 15 or higher, making it easy to add sunscreen to a daily skincare routine. 

Sunscreen Selection and Application: Factors to Consider 

To get the maximum protection from your sunscreen, it’s important to apply it properly. The FDA recommends applying sunscreen fifteen minutes before sun exposure. 

Be sure to apply a generous amount on all parts of the skin not covered by clothing. A good rule of thumb is to use at least one ounce (equivalent to a shot glass full) to cover your whole body. You’ll need to reapply every two hours, as well as after “swimming, sweating or toweling off.” 

Sunscreens have expiration dates. If you don’t see one listed on the bottle, you can usually expect a shelf life of up to three years, provided the product hasn’t been repeatedly exposed to high temperatures.  

One should also consider product’s SPF. It may seem as though a product with an SPF of 100 would offer double the protection of a product with an SPF of 50, but that’s not really the case. According to the Environmental Working Group (EWG), high SPF sunscreens only offer slightly more protection: SPF 30 blocks nearly 97% of UVB radiation, SPF 50 blocks about 98% and SPF 100 blocks about 99%. The Skin Cancer Foundation also notes that higher SPF products may provide a false sense of security, prompting people to stay out in the sun longer or not reapply as often. 

The FDA recommends using an SPF of at least 15. If you have fair skin, you may want to consider an SPF between 30 and 50. Anything higher than 50 is not likely to provide much additional protection. 

Last but not least, don’t forget that sunscreen is not the only way to protect yourself from the sun. In fact, sunscreen works best when used in tandem with other methods such as hats, sunglasses, protective clothing and umbrellas and other sources of shade. 

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