Warning: This post features graphic sunburn imagery.

We’ve made it a week into summer and it's time for a little seasonal reminder: wear sunscreen, and apply it frequently. This advice isn't limited to when you're at the pool or on vacation, either.

Just ask Julie Nisbet, whose severe sunburns landed her in urgent care.

Nisbet is a marathon runner based in England. She recently went on a 21 hour, 69-mile run that left the skin on her legs burning, according to a report by Buzzfeed. buzzfeed.com - buzzfeed.com

Despite stopping on occasion to apply SPF 30, Nisbet came out of her trek with a sunburn on her legs that initially manifested in small blisters that eventually expanded into giant, painful blisters that required medical attention.

buzzfeed.com - buzzfeed.com

The blisters were drained and the runner is now recovering from the burns. She will spend weeks with legs bandaged in order to properly heal, Buzzfeed reports.

While Nisbet seemed to do everything right, her situation highlights that it's important to repeatedly apply sunscreen.

Nisbet wore a sunscreen with a sun protection factor (SPF) of 30 or higher, which is what dermatologists recommend.

Where she may have gone wrong is in the application: as the American Academy of Dermatology (AAD) notes, sunscreen should be applied to any skin exposed to the sun every two hours and after swimming or sweating. Every person is at risk and, as the AAD notes, you should apply “1 ounce, enough to fill a shot glass” to an exposed part of the body.

This may seem like common sense but it really isn’t. Studies have found that most Americans don’t use sunscreen. In fact, the AAD found that only 14 percent of men and 30 percent of women say they regularly apply sunscreen when their face or skin is exposed to the sun.

Moreover, people apply less than half of the recommended amount of sunscreen needed to protect the skin, according to a study by researchers with Population and Clinical Sciences Division at Queensland's Institute of Medical Research. Areas that frequently are forgotten include obvious places like the ears but also eyelids, lips, scalp, and tops of feet.

Yes, this is obvious, but poor protection from the sun can cause burns, blisters, and can even lead to skin cancer.

Ultraviolet (UV) rays are a known carcinogen. Sunscreens—particularly broad spectrum sunscreens—work by absorbing or reflecting UV rays.

If you repeatedly neglect to protect your skin from the sun, you risk developing skin cancer. You may also experience premature skin aging, lesions, and even eye damage from extended UV exposure.

So, again, friendly Summer reminder: wear sunscreen or you will literally get burned.

buzzfeed.com - buzzfeed.com
As for Nisbet, she learned her lesson—and will not repeat this Summer mistake. “I didn't pay enough attention during that race to reapply suncream,” she told Buzzfeed. “It's been a harsh lesson to learn."