Can sunscreens become carcinogenic over time?

Sunscreens are regarded as one of the most effective tools to protect skin from the harmful effects of solar radiation. These rays cause various types of cellular damage, including DNA mutations, alterations to structural proteins such as collagen and elastin, and skin inflammation. Over time, these changes accelerate the skin aging, and notably increase the risk of skin cancer. In response, public health agencies recommend protecting against sun exposure by avoiding extended direct exposure, especially between 11 a.m. and 4 p.m., wearing long clothing, and using a sunscreen with a high SPF. Despite these benefits, some concerns remain, and sunscreens are sometimes suspected of becoming carcinogenic over time.

Current scientific data do not support that sunscreen use increases skin cancer risk; they indicate the opposite.

A 2014 meta-analysis pooled results from 21 studies involving 7,150 malignant melanoma cases. Using regression, researchers demonstrated that sunscreen use did not increase melanoma risk, even with long-term use. In reality, studies show a significant protective effect of sunscreens against skin cancers. One robust piece of evidence comes from a randomized controlled trial in Australia. Over 4.5 years, 1,621 adults were followed to assess the impact of daily use of a broad-spectrum SPF 15+ sunscreen.

In this protocol, volunteers were divided into two groups: one applied sunscreen daily, while the other used it at their discretion, or not at all for some participants. At the end of the trial, the daily use group showed a 40% reduction in squamous cell carcinoma incidence compared with the control group. The protective effect persisted after the intervention. Eight years after the protocol ended, the daily use group still showed a 40% reduction in squamous cell carcinoma incidence. This sustained effect reflects that more participants in this group maintained regular sunscreen use after the trial.

Far from increasing the risk of skin cancer, the regular and rigorous use of sunscreen is a effective prevention tool.

When discussing potential toxicity or carcinogenic risk of sunscreens, the ingredient most often implicated is octocrylene, a chemical filter targeting UV rays. Beyond carcinogenicity concerns around this compound, its ability to undergo a retro-aldol reaction and convert into benzophenone raises concern. This reaction is favored by heat and light and occurs during storage at room temperature.

The benzophenone formed in this way is concerning, as it is classified as a suspected carcinogen (category 2 in Europe) and a potential endocrine disruptor.

Studies have confirmed benzophenone accumulation in products containing octocrylene. For example, chemical analysis of 28 cosmetics containing octocrylene revealed the presence of benzophenone in all products, at concentrations above 10 ppm (0.001 %). Benzophenone concentrations increased with time and temperature, indicating continuous octocrylene degradation in formulations.

Benzophenone has been studied for its potential to influence tumor development. A 2008 study showed that exposing human lung cancer cells to low concentrations of benzophenone induced an epithelial-to-mesenchymal transition, a process that makes cells more aggressive, facilitating their migration, invasion capacity, and, ultimately, metastasis formation. In mice, other research highlighted a role for benzophenone-3 in breast tumor progression: increased cell proliferation and reduced tumor cell apoptosis were observed. It is essential to note that these results were obtained under specific doses and experimental conditions often distant from realistic human skin exposure.

In addition to benzophenone and octocrylene, other UV filters are under regular scrutiny for potential carcinogenicity, including ensulizole, homosalate, octinoxate, and octisalate. Available scientific data remain insufficient to confirm that these filters are carcinogenic. A recent review focused on these six sunscreen agents. It analyzed data from several dozen studies conducted in vivo, in vitro and in silico and conducted a margin of exposure assessment, defined as the difference between the dose at which a toxic effect occurs and the dose absorbed by humans. The review concluded that none of these filters was genotoxic and that there was no evidence suggesting a carcinogenic mechanism relevant to humans. Systemic exposure levels measured in humans remain below concentrations at which biological activity is observed in laboratory settings.

Although more research is needed before the carcinogenic potential of UV filters can be assessed, current data do not support the conclusion that they make sunscreens carcinogenic. The benefit-risk ratio favors daily sunscreen use to prevent skin cancer.

Find here Typology sun care products formulated with the UV filters that are the most well-documented for both human safety and ecotoxicology.