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We all already know that tanning beds are bad and that soaking up faux sunshine puts you at higher risk for skin cancer. Those of us who participated in the tanning salon craze of the 2000s (guilty), have been reckoning with that for years. But a new study from Northwestern Medicine and the University of California, San Francisco reveals that the cancer risk from tanning beds is even worse than we ever knew—uniquely bad, in fact.

Let's start with what we already knew: If you've used a tanning bed at any point in time, you've increased your risk of melanoma, the deadliest form of cancer. Before now, the belief was that indoor tanners were 74 percent more likely to develop melanoma than those who have never tanned indoors, and that just one session in a tanning bed could increase the risk by 20 percent. But this new research suggests that tanning bed usage actually triples the risk of skin cancer—a 200 percent increase. It also offers new insights on the alarmingly unique way tanning beds cause cancer.

The study analyzed thousands of medical records, comparing melanoma rates in tanning bed users versus non-users. Researchers also used single-cell DNA sequencing to investigate 182 skin biopsies from tanning bed users and control subjects on a cellular level. Its findings show that the UV light from tanning beds mutates skin cells and causes “melanoma-linked DNA damage across nearly the entire skin surface.”

It’s already a known fact that indoor and outdoor tanning alike can cause DNA damage, but what these new findings tell us is that the DNA damage caused by tanning beds is on a wholly different level compared to regular sun exposure. “This study is interesting in that it shows more mutations and unique mutations associated with tanning beds [than previously known],” says Caren Campbell, MD, a board-certified dermatologist in San Francisco. “Genetics put us at risk, and then high-risk behaviors put us at risk for cancers. At a DNA level, [tanning bed use] is a high-risk behavior, which we knew, but this proves… it's changing the DNA.”

According to Mona Gohara, MD, a board-certified dermatologist and clinical professor at the Yale School of Medicine Department of Dermatology, a cell mutation is a “permanent mistake” in a cell’s DNA. “Think of DNA like a spell-check for your skin: when tanning beds hit cells with intense UV radiation, they introduce typos. Most typos are harmless, but some land in dangerous places—genes that control growth—and that’s where cancer can begin,” she says. “This study shows tanning bed users had twice as many of these dangerous typos as non-users, which helps explain why their melanoma risk is so much higher.”

“The takeaway is simple: tanning beds don’t just age your skin, they biologically shift your cells toward cancer.”

As we know, skin cancer is generally identified via moles and other skin lesions, but the study found that DNA changes among tanning bed users were present in areas of the skin that looked entirely normal. “Even in normal skin from indoor tanning patients, areas where there are no moles, we found DNA changes that are precursor mutations that predispose to melanoma,” Pedram Gerami, MD, a professor of skin cancer research at Northwestern University Feinberg School of Medicine and one of the study’s authors, shared in a press release. “That has never been shown before.”

It’s an unsettling finding, Dr. Gohara says. “It means tanning beds don’t just damage the skin you expect, like spots with visible sun exposure or moles; they quietly alter the DNA across nearly the entire skin surface, even in areas that look unaffected.” And, of course, when there’s nothing notable or suspicious happening on the skin’s surface, cancer is more difficult to detect, diagnose, and therefore treat. “Second, it reinforces why full-body skin exams matter so much,” Dr. Gohara adds, “Cancer doesn’t always announce itself where you’re watching—it can start backstage long before it shows up under the spotlight.”

Tanning in the sun, of course, still presents skin cancer risk, but the study findings show that there’s a significant difference between the effects natural sunlight and the artificial light of a tanning bed. “For years, the tanning industry argued that beds were no worse than sunlight,” Dr. Gohara says. “This research irrefutably shows that indoor tanning causes broader, more intense DNA damage than everyday sun exposure.”

The study also noted that tanning bed users were more likely to develop melanoma in places that aren’t typically impacted by everyday sun exposure, like the buttocks and lower back, because most tanning bed users tan naked or in their underwear. “In my dermatology practice, I see multiple skin cancers every single day,” says Laurel Geraghty, MD, a board-certified dermatologist in Oregon. “I've seen a handful of melanomas on the buttocks of young women—every one of them has used tanning beds.”

Many of us have given up the tanning bed habit, but that doesn’t mean tanning beds are a thing of the past; people still tan despite knowing the (many, many) risks. If you’re one of those people, consider Dr. Gohara’s input: “The takeaway is simple: tanning beds don’t just age your skin, they biologically shift your cells toward cancer.”