The sunscreen myth: could it really be causing skin cancer? | Melissa Davey

Because of his job as a dermatologist, Dr Deshan Sebaratnam frequently gets asked questions by friends, family and strangers about skin treatments. But lately, he says, he has been confronted by “a lot of myths around sunscreens”, especially on his social media feed.

Among the most frequent is “that sunscreen can actually cause skin cancer”, says Sebaratnam, a conjoint associate professor at the University of New South Wales.

Dr Michelle Wong, a chemist, says the myth largely comes from concern about benzene, a contaminant (not an ingredient) found in some sunscreens and other products such as sanitisers and dry shampoos, which led to product recalls in 2022.

What does the evidence say about benzene?

“While it’s a known carcinogen, the likelihood of cancer actually forming depends on the amount you’re exposed to,” Wong says.

The amount of benzene found in the consumer products recalled was minuscule, with the highest levels (six parts per million, or 6ppm) reported in a sunscreen tested by Valisure.

Even then, Martyn Smith, a professor of toxicology at the University of California, calculated that 10ml of contaminated sunscreen would – in the very worst case scenario – result in absorbing the amount of benzene people are exposed to from breathing in city air for half a day.

“Benzene is a common air pollutant, an additive to petrol, and is produced by gas stoves,” Wong says. “Benzene doesn’t get through skin easily – only about 1% is absorbed. The main route of exposure is inhalation.”

One group of dermatologists found sunscreen users actually had lower blood benzene concentrations compared with those who said they never used sunscreen, suggesting petrol emissions and secondhand smoke have a bigger impact.

Despite this, fear-mongering about benzenes in sunscreen and cancer risk continues to be spread on social media.

“Australia is the skin cancer capital of the world,’ Sebaratnam says. “An Australian dies of melanoma every six hours. Skin cancer is one of the most preventable cancers and there is excellent evidence from many scientific studies that sun protection, including sunscreen, helps minimise this risk.”

Wong, who helps to dispel misinformation about cosmetic products through her Lab Muffin website, says she has seen some brands promote their products as “benzene-free” even though no brand deliberately adds the contaminant.

“Claiming to be benzene-free is honestly probably impossible, given how ubiquitous it is everywhere, as there’s probably at least a few molecules in any sunscreen that’s exposed to air,” she says.

So should I wear sunscreen?

Sunscreen, when used appropriately, has “never led to anything other than a decrease in skin cancer rates by a considerable margin”, says Prof David Whiteman, a medical epidemiologist and cancer control expert at the QIMR Berghofer Medical Research Institute.

Despite this, he says he often gets asked about higher rates of skin cancer being found among sunscreen users. “The sunscreen is not causing the cancer,” Whiteman says.

“It’s like people who wear bulletproof vests are more likely to die from a gunshot wound. It’s because you only wear a bulletproof vest when you’re going into a place where you might get shot, and sometimes you’re just shot in a place that’s not protected by the bulletproof vest. It’s the same with sunscreen.

“People don’t put sunscreen on if they’re going to the theatre at nine o’clock at night. People only put on sunscreen when they’re going out in the sun. So there’s a direct association between using sunscreen, and being exposed to the hazard.”

Prof Anne Cust, the chair of Cancer Council’s national skin cancer committee, says the drug regulator the Therapeutic Goods Administration uses “a very conservative approach to set limits for benzene”.

“These limits are based on the potential health impacts to an individual of using the maximum recommended amount of a product that contains more than two parts per million of benzene every day for 70 years,” she says. Products are recalled out of an abundance of caution and not because of significant risk, she says.

“Australians should feel confident in the efficacy and safety of approved sunscreens they’re using.”

A myth that she would like to see dispelled is that the SPF in cosmetic products such as makeup will provide enough protection from UV exposure. In reality, most cosmetic products don’t offer enough protection, so Cust says it’s recommended to wear a sunscreen that is SPF50 or SPF50+ underneath makeup.

“Sunscreen should be applied 20 minutes before going outdoors, and for an adult, recommended sunscreen application is approximately one teaspoon for each arm, leg, body front, body back and face, including neck and ears,” she says.

“Sunscreen needs to be reapplied at least every two hours, irrespective of the water resistance of the sunscreen, and should be reapplied after swimming, sport, sweating and towel drying.”

• Melissa Davey is Guardian Australia’s medical editor. She has completed a master of public health and moonlights as a fitness instructor

• Antiviral is a fortnightly column that interrogates the evidence behind the health headlines and factchecks popular wellness claims