Influencers are saying sunscreen causes cancer. they are wrong.

“Do you wear sunscreen?" reads a caption in the video, which has more than one million views on X. No, the woman responds. A new caption appears: “There is no PROOF the sun causes cancer."

The 15-second video is a glimmer of the anti-sunscreen sentiment emanating from some influencers and celebrities. Their claims, debunked by dermatologists and scientists in other videos, range from misconceptions that sunscreen itself causes cancer to conspiracies that sunscreen is a ploy by pharmaceutical companies to pad profits and sicken people.

Recalls of some spray sunscreens after a testing company detected contamination of benzene, a chemical that can cause cancer, have also fueled skepticism. “We are literally rubbing cancer into our skins," one TikTok user said in a viral video last year.

Some wellness influencers tout the sun’s natural healing powers. Others tell their followers to make homemade sunscreen or that sun protection prevents people from producing the vitamin D that they need. Consuming seed oils is what really causes sunburns, some say.

In fact, sunburn is caused by the sun, dermatologists confirmed. Sensibly using sunscreen is far safer than excessive sun exposure, they said. Broad-spectrum sunscreen protects skin from ultraviolet radiation that can cause sunburn, skin cancer and signs of aging. Health agencies in the U.S. and elsewhere list sunscreen as crucial in preventing skin cancer.

Cosmetic chemist Michelle Wong, who debunks misconceptions about sunscreen under the online handle “Lab Muffin Beauty Science," said myth-busting has become a full-time job. In a recent 46-minute YouTube video, Wong breaks down claims that sunscreen doesn’t help prevent skin cancer and that seed oils cause sunburns.

The long, obscure names of sunscreen ingredients can help people conclude they are nefarious, Wong said: “Sort of like stranger danger, essentially."

Maggie Dudeck didn’t wear sunscreen growing up in Hawaii or while she played tennis for California State University, Los Angeles. The 41-year-old content creator used tanning beds in her 20s. A couple of years ago, a biopsy of a bump on her nose showed basal cell carcinoma. In a video last year, Dudeck showed images of her surgery and recovery with a clear message: Sunscreen didn’t cause her cancer—the sun did. Excessive sun exposure and tanning beds can increase risks for basal cell carcinoma, according to the American Cancer Society.

“I’m not a doctor," Dudeck said, “but I can tell you that I know I got skin cancer from not wearing sunscreen."

About a quarter of adults under 35 think drinking water can help ward off sunburns, and one in seven believes applying sunscreen daily can cause more damage than sun exposure, a recent survey conducted by the Orlando Health Cancer Institute found.

Some celebrities share those misconceptions, too. Kristin Cavallari, who starred in the reality show “Laguna Beach," recently said she doesn’t wear sunscreen. In his 2017 book, Tom Brady said drinking water helps him prevent sunburns.

“Those things may have certain health advantages," said Dr. Rajesh Nair, an oncology surgeon with the Orlando Health Cancer Institute. “They certainly don’t do anything to help protect our skin from damage—certainly not from the effects of UV radiation."

Dermatologists said it is unlikely people can put on enough sunscreen to entirely prevent adequate vitamin D production in their skin. Vitamin D, which supports bone health and immune function, can also be found in supplements and foods including fish.

The benefits of sunscreen aren’t one-size-fits-all. There is little evidence ultraviolet radiation exposure is associated with melanoma in nonwhite people. They are at lower risk of developing skin cancer and need more sun exposure to generate adequate vitamin D than white people, said Dr. Adewole Adamson, a dermatologist and assistant professor of internal medicine at the University of Texas at Austin Dell Medical School. For people with darker skin tones, sunscreen is more a tool for preventing wrinkles and other signs of aging, he said.

U.S. health officials tell people broadly to wear sunscreen to protect against the harmful effects of the sun. The American Academy of Dermatology recommends people apply one ounce of broad-spectrum sunscreen with an SPF of at least 30 on parts of the body that aren’t covered by clothing.

In Australia, new guidance is tailored to UV indexes and skin type. “They’re actually letting the data guide how they’re making recommendations instead of a one-size-fits-all approach," Dr. Adamson said.

The Food and Drug Administration classifies sunscreens as over-the-counter drugs. The agency has conducted studies demonstrating that common sunscreen ingredients are absorbed into the bloodstream at high levels. The FDA is seeking additional safety data from companies on active ingredients including oxybenzone and avobenzone. Those active ingredients have been used in sunscreens for decades with no evidence of harm in humans, dermatologists said.

“Just because it’s there doesn’t mean it’s doing anything bad," said Dr. Adam Friedman, chair of dermatology at George Washington University School of Medicine and Health Sciences.

Oxybenzone, an ingredient in some sunscreens approved in the U.S. for more than four decades, has drawn particular interest from people concerned about absorption. One study found rats experienced endocrine disruption after eating large amounts of oxybenzone for several days.

Even if humans applied sunscreen containing oxybenzone over their entire bodies every day, it would take more than three decades to reach a similar level of exposure, a 2011 study found.

People who don’t want sunscreen absorbed into their skin can use other products containing zinc oxide and titanium dioxide that stay on the surface, said Dr. Heather Rogers, co-founder and co-owner of Modern Dermatology, a Seattle-based practice.

“That entire argument goes away if you use zinc," Rogers said.

Write to Jennifer Calfas at jennifer.calfas@wsj.com