How often should you reapply sunscreen? Maybe not as much as you think

Sunscreen is key to protecting yourself from sunburns, skin cancer and visible skin aging, but it isn’t a one-and-done process.

Health Canada advises using a broad-spectrum sunscreen with a minimum SPF (sun protection factor) of 30 at least 15 minutes before going outside and reapplying every two hours during sun exposure. While that’s a good general rule of thumb, there are other factors to take into consideration.

So, how often should you be reapplying throughout the day? Maybe not as much as you think.

“There have been papers that show that if you’re sitting under a tree and not doing much — not sweating, not playing tennis, not swimming — you probably don’t need to reapply that often,” said Dr. Cheryl Rosen, head of the division of dermatology at Toronto Western Hospital and University Health Network.

In addition to outdoor activities, Rosen noted that the time of year can also impact how often and where on the body sunscreen should be applied.

“If you’re skiing in the winter, truly you only need to put it on your face because that’s the part that’s going to get the wind and the sun,” she said. “In the summer, you need to reapply if you’re swimming, if you’re water skiing. If you’re out in the sun sweating a lot, yes, reapply.

“I think people just need to be aware. It’s not a bad idea to, for instance, if you’re swimming, wear a UV shirt so you don’t have to bother putting sunscreen on your back and your arms. … Wearing a hat is a good idea to protect your neck and your ears. I think it makes sense to sort of be aware of your surroundings and reapply — I mean, the government says every two hours, but you may not need to do it that often depending on your activities.”

Another thing to be mindful of when applying and reapplying sunscreen is how much of the product is being used. Health Canada recommends that adults use one teaspoon for every body part exposed to the sun — including ears, scalp and the backs of your hands — though people may need more or less of that amount depending on various factors, says Lisa Heggie, founder and owner of Canadian sunscreen brand KINeSYS.

“The teaspoon is a useful guide, but there isn’t a magic amount that works for every person or situation,” said Heggie. “How much skin is exposed, body size and whether you’re wearing sun-protective clothing all make a difference. Some people may need more than one teaspoon; some may need less. The bigger issue is that people tend to under-apply and, more importantly, don’t reapply often enough.”

To ensure the right amount of sunscreen is distributed onto exposed skin, Heggie recommends opting for a lotion over aerosol sprays.

“With aerosol sprays, it can be harder to get enough product evenly onto the skin, particularly outdoors or in windy conditions. Without adequate, even coverage, you won’t get the level of SPF protection shown on the label,” she said. “Lotion allows you to see where you’re applying it, while a pump spray gives you a more targeted application.

“Whichever format you use, I recommend swiping it over the skin. Personally, I like two lighter coats. Just like painting, it helps give more even coverage and catch spots you may have missed.”