This story has been updated.
But, rather than applying “too much” sunscreen, Sass is instead following Food and Drug Administration guidelines for testing sunscreen protection factor (SPF), which means a lot of his sunscreen review followers are probably applying too little. Experts recommend applying the equivalent of a shot glass of sunscreen (approximately an ounce) for the entire body.
Skin cancer is the most common form of cancer in the United States — nearly 100,000 people in the United States are expected to be diagnosed with melanoma this year — and sunscreen has been shown to help prevent early signs of aging and damage that can lead to skin cancer, but that’s only if you apply it correctly and reapply it often.
“When a sunscreen brand does a photo shoot and they use a teardrop amount [of sunscreen] on a model’s cheek, people then think that’s how much they should use, and they end up getting sunburned,” said Sass, a biomathematics and statistics PhD candidate at North Carolina State University who maintains a free database of more than 200 sunscreens.
Evidence suggests that people tend to use less than half of the recommended amount of sunscreen (the same study showed it’s common for people to burn from “missing a spot” and waiting to apply sunscreen until they are outside).
One sunscreen application doesn’t give you “carte blanche to go sit in the sun for eight hours,” said Jennifer Lin, a dermatologist and co-director of the Melanoma Risk and Prevention Clinic at Brigham and Women’s Hospital in Boston and an assistant professor at Harvard Medical School.
How often should you reapply?
The American Academy of Dermatology recommends reapplying sunscreen of at least 30 SPF every two hours outdoors, although Lin said it could be more often if you spend prolonged time outdoors.
“Think of your sunscreen as a constantly waning force field, particularly chemical [nonmineral] sunscreens‚” Lin said. Sweating, swimming and rubbing off on fabrics all weaken the force field.
There are three types of skin cancer: Basal cell and squamous cell carcinoma are the two most common; melanoma is not as prevalent but is far more dangerous. Research suggests that intermittent high doses of ultraviolet (UV) radiation can lead to melanoma while cumulative everyday exposure is associated with carcinoma.
“The science is very strong that extensive sun exposure causes damage to the skin,” said Henry Lim, a Detroit-based dermatologist and specialist in dermatology immunology. This ranges from wrinkles and precancerous rough spots to the development of skin cancer. “We also know that with proper photoprotection, we can decrease the probability of sun damage.”
Sunscreen should be combined with seeking shade and wearing sun-protective clothing, sunglasses and a hat, said Ranella Hirsch, a dermatologist in Cambridge, Mass. “Sunscreen was not meant to stand alone as the only warrior in this battle.”
Hirsch’s warrior of choice for kids is a sunscreen stick. “It makes things neat and easy.” Hirsch trained her children to use a stick when they were preschoolers. She recommends swiping three to four passes on each exposed body part with a 25 percent overlap.
One of the reasons skin cancer is so common in the United States, Hirsch said, is because our fundamental approach to sun protection differs from other countries. “Americans think of sunscreen more as ‘I’m going to the beach, so I’ll throw my sunscreen in the bag,’ rather than applying it every day like in Asia and Australia.”
And, despite the overwhelming evidence for sun caution, Gen Z still wants to tan. On TikTok, #tan had notched up 2.7 billion views as of last week and included videos of young people showing off their tan lines, advertising sun-amplifying products and posing inside tanning beds. (Strong evidence exists that indoor tanning increases the risk of melanoma and non-melanoma skin cancers.)
“Any type of tanning is an indication the skin is undergoing damage,” Lim said.
He also advises against substituting coconut oil for sun protection. “No data shows that coconut oil can protect the skin,” Lim said. “Because coconut oil is moisturizing, it could enhance the penetration of UV into the skin.”
Jennifer Bowers, a cancer prevention fellow and psychologist in the National Cancer Institute’s Basic Biobehavioral and Psychological Sciences Branch, focuses her research on suntanning behaviors in college students, who are considered a high-risk population because they spend more time in the sun than older people.
One of Bowers’s main research areas is unintentional tanning in young people. “We found that indoor tanning has gone down in the past few years, but rates of melanoma are still rising,” she said, which prompted her to look deeper into unintentional tanning. “I heard from participants in my studies that they could get tan from walking across campus or doing errands and things like that.”
Bowers recommended setting reminders for yourself to reapply sunscreen. “It’s about building a habit to protect yourself.”
The experts agreed that the best sunscreen is the one you will use consistently.
“UV radiation is getting stronger because the ozone layer is getting thinner,” Lin said. “So, if anything, sun protection will become more and more relevant for us as a species.”
Janna Mandell is a freelance reporter based in the San Francisco Bay area.