Sunscreens
The use of sunscreens has long been advised when spending any significant time out in the sun, as it has long been accepted that prolonged exposure to intense sunlight will raise the risk of skin cancers. However, recent studies question the previously assumed value of simply slapping on sunscreen and assuming that any amount of sun exposure will have no effect.
In fact, there is some indication that the sunscreens themselves may contribute to cancer. One study from the journal Cancer Epidemiology, Biomarkers & Prevention, looking at genetic damage in cancer victims in the United Kingdom, noted that sunscreen usage was paradoxically associated with a much greater risk of cancer, particularly skin cancers.
While a number of rationalizations have been proposed for this finding, such as neglecting to reapply the sunscreen during the day or increased usage after a cancer diagnosis, these hypotheses have yet to be tested. But there are other explanations that involve the sunscreen itself.
First, sunscreens are rated by their ability to block the ultraviolet radiation that causes sunburns. But in doing so, you also inhibit vitamin D formation, which is an essential component of immune function, including the suppression of cancer growth. While it is probably unlikely that you would use enough sunscreen to block a reasonable amount of vitamin D production while spending a day at the beach, this could be a factor in someone who conscientiously applys sunscreen when outdoors for much shorter periods of time, when their lifestyle already renders them deficient in vitamin D.
Secondly, and probably more significant, is the fact that most sunscreens contain chemicals that are already known to promote cancer development.1 An earlier work published in the Journal of the American Medical Association found that such chemicals are quickly absorbed, producing blood levels that exceed (in some cases, greatly) the maximum FDA regulations for that compound after just one application.
Whatever the reasons, here are the findings of that study that involved 470,000 people in the United Kingdom:
| Type | Increased Risk2 |
|---|---|
| Melanoma | 292% |
| Basal Cell Carcinoma | 140% |
| Squamous Cell Carcinoma | 126% |
1Some of these are encamsule, octocrylene, oxybenzone, octinoxate, octisalate, homosalate and avobenzone.
2Compared to non-sunscreen users.
See also:
- Analysis of the UK Biobank study by Nicolas Hulscher, MPH
- Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation: The presence of zinc oxide can cause toxic degradation of other sunscreen components after 2 hours.