Why a higher SPF doesn’t necessarily mean more sun protection

SPF 30 is a good choice for a day at the pool. Aleksej Sarifulin/Getty Images
  • SPF measures how much UVB radiation sunscreen blocks from hitting your skin.
  • But the higher the SPF number, the less protection it offers from UVA radiation.
  • You should be using a broad-spectrum, SPF 15 sunscreen for everyday use – just up it to SPF 30 if you know you are going to be spending a lot of time outside in direct sunlight.
  • This article was medically reviewed by Debra Jaliman, MD, a board-certified dermatologist with a private practice in New York City
  • This story is part of Insider’s guide on How to treat sunburn.

With so many options for sunscreen these days, how do you choose the one that’s going to best protect you from sunburn? The first step is checking out the SPF, short for Sun Protection Factor.

Most experts will recommend an SPF of 30 or higher if you’re spending a lot of time in direct sunlight. However, a higher SPF doesn’t necessarily mean more overall protection. Here’s what you need to know.

SPF measures UVB radiation protection

Most sunscreens are formulated to block two types of harmful UV radiation:

  • UVA rays, which penetrate deeper and cause wrinkles, dark spots, and premature ageing.
  • UVB rays, which cause sunburns and tanning.
  • Both types can cause skin cancer.

SPF is a measure of how much UVB radiation a sunscreen blocks from your skin:

How many UV rays each SPF blocks

But this doesn’t necessarily mean that a higher SPF is better. In fact, “as the SPF number goes up, protection against UVA goes down because of the way that the protective ingredients in the sunscreen interact which is why SPF 100 is not recommended,” says Orit Markowitz, MD, Director of Pigmented Lesions and Skin Cancer at Mount Sinai.

How to choose the right SPF

According to the Skin Cancer Foundation, SPF 15 sunscreen is the best choice for normal tasks. It’s ideal for doing things like walking your dog or running errands.

But if you plan to do any outdoor activities like hiking or swimming, be sure to go for SPF 30. And make sure you always stick to a broad-spectrum sunscreen.

Broad-spectrum sunscreens protect against both UVA and UVB rays. If you don’t see broad-spectrum on the label, then the sunscreen may not protect you from UVA rays.

How to choose the right sunscreen

It’s best to avoid aerosol sunscreens since researchers have found that most people who use spray sunscreen only apply 25% of the needed amount. In fact, in order to get proper coverage from spray sunscreens, you’d need to spray each area – legs, feet, back, arms, shoulders, etc. – for up to six seconds, according to Harvard Medical School.

Instead of sprays, choose thick lotions and slather them on 15 minutes before you go outside to let them soak into your skin.

Regardless of what SPF you’re using, you should reapply sunscreen every two hours if you’re spending a lot of time outside. Also, make sure the sunscreen is water-resistant if you know you’re going to be sweating. If you just went swimming, apply immediately after since water-resistant does not mean waterproof.

You can also take other precautions while outdoors, such as wearing protective clothing like long sleeves or wide-brimmed hats. And if you can, stay out of the sun during peak hours of sunlight, which tend to be between 10 a.m. and 4 p.m, though this may vary depending on your location and time of year.

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