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The data on sunscreen use and cancer risk are complex, but on balance suggest that the short-term and long-terms benefits of sunscreens significantly outweigh their risks when used during periods of unavoidable exposure.

A reader asked me to look into the claims that sunscreens cause cancer, especially the claims made by Elizabeth Plourde. When our own Scott Gavura evaluated sunscreens , he concluded:

Elizabeth Plourde thinks otherwise. She says sunscreens don’t work to protect from skin cancer; in fact, they cause cancer (not just skin cancers, but breast, prostate, and other cancers). Her book Sunscreens Biohazard: Treat as Hazardous Waste accuses sunscreens of all manner of evils, everything from causing infertility to destroying coral reefs. She even implicates sunscreens as a cause of autism. She is not the only one to raise these issues, but she has written the most comprehensive critique of sunscreens, with over 500 references. I wanted to give her a fair hearing, and the book was not available through my library or even through inter-library loan, so I bit the bullet and sacrificed $9.98 of my hard-earned money for the Kindle version and read it. I learned a few things, but I didn’t find her evidence or her reasoning convincing.

An epiphany based on a false observation and a single study

She starts by describing the epiphany that led to her investigations. She had read that coral reefs were dying due to global warming; but when she went swimming in Hawaii, she thought the water felt colder than ever before in her 40 years’ experience of swimming there. She didn’t question the validity of her subjective impression; if she had, she might have learned that sea temperatures in Hawaii are actually rising. Anyway, she assumed global warming couldn’t be the cause of coral die-off, and she quickly found another explanation: an article “unequivocally demonstrating” that coral die from exposure to sunscreen chemicals. She says she “immediately” knew she had to write a book warning the world that sunscreens were threatening not only coral reefs but the whole marine habitat. Seems like a bit of a leap to me! As she combed the scientific literature in search of confirmation, she found that birds, mammals, and humans were also under threat.

I looked up the article that had impressed her so much. It was not the unequivocal proof she thinks it was. The researchers added varying amounts of sunscreen to plastic bags of seawater containing nubbins of coral organisms. The concentration of sunscreen they used was higher than most reported environmental levels, and the bleaching they found was not dose-dependent. The mechanism? Sunscreen apparently promoted a lytic cycle in viruses latent in the coral. They estimated that up to 10% of the world’s reefs are potentially threatened by sunscreen-induced coral bleaching. I don’t think that conclusion is warranted by their data. And it’s only a single laboratory study that has not been replicated.

Why she thinks sunscreens don’t work

She argues that if sunscreens really worked, the incidence of skin cancer would have dropped by now, as the use of sunscreens has become ubiquitous. She reports that studies have shown both increases and decreases in the incidence of skin cancer, but then she claims that there has been “a tremendous and consistent rise.” Her citation for this says nothing of the sort. It does say the results of studies are controversial, with some showing a protective effect of sunscreen and others suggesting a significant risk.

Even if the incidence of skin cancers has risen, that’s not evidence that sunscreens don’t work, or that they cause skin cancer. There could be other reasons, confounding factors, to explain the rise. It might be that people are spending more time in the sun because sunscreens give them a false sense of security; it might be that they are not using sunscreens properly or reapplying them when needed; it might be that they are using older UVB sunscreens that don’t protect from UVA; it might be due to other factors like depletion of the ozone layer, longer lifespans, increased popularity of outdoor activities, exposed skin due to clothing style, use of tanning beds, earlier detection of skin cancer, etc. Plourde’s reasoning is faulty and is unworthy of a scientist.

One of her references says:

Whereas chronic sun exposure is the main cause of NMSC [non-melanoma skin cancer], the development of melanoma appears to be related to intense, intermittent sun exposure. Ozone depletion has contributed to rising incidence rates of both NMSC and melanoma. In contrast to NMSC, there is not a direct relationship between ultraviolet radiation and melanoma.

Nowhere does Plourde even mention ozone depletion. Her review of the literature seems to be aimed at finding justification for her pre-conceived ideas, not at searching out the truth.

Sunscreens not associated with melanoma

She thinks sunscreens cause melanomas. The article she incorrectly cited for incidence found that the data “do not suggest a causative association between sunscreen use and melanoma.” Meta-analyses like this one have confirmed that there is no association between sunscreen use and melanoma.

The various types of sunscreen

Plourde does a good job of describing the various sunscreen ingredients and the difference between UVA and UVB protection. She provides a comprehensive list of existing sunscreens and explains that newer sunscreens are safer and more effective for blocking both UVA and UVB. She mentions that other sunscreens are being developed; but she discourages early adoption, since she says it has taken 30 years to identify the harms from older products.

Sunscreens were originally marketed to prevent sunburn, not cancer. In Europe, they are regulated as cosmetics, while in the US they are considered drugs. They are rated by SPF (sun protection factor) but this only applies to UVB; there is no good way to rate UVA sunscreens.

The American Academy of Dermatology recommends everyone use a sunscreen that provides:

Broad-spectrum protection (protects against UVA and UVB rays)

SPF 30 or higher

Water resistance

Endocrine disruptors?

She says sunscreens contain endocrine disrupting chemicals that can have estrogenic, androgenic, anti-estrogenic, and anti-androgenic effects. She provides plentiful evidence for these effects in laboratory rats, but no evidence for significant effects in humans. She provides evidence for endocrine effects in fish in the lab, but then she assumes that intersex fish and other reproductive anomalies found in nature are a result of the minuscule amounts of sunscreen chemicals that have been detected in our oceans and streams. She cites changing statistics for male infertility, cryptorchidism, hypospadias, testicular cancer, breast reduction surgeries in men, and the timing of puberty. She suggests that all of these could be caused by sunscreens, but there is no evidence that they are.

Other concerns

She speculates that sunscreens could be contributing to other health problems like breast cancer, thyroid disorders, and obesity. She sees “connections” between the rise in autism and the rise in sunscreen use. She says those connections make it imperative to do more research to find out if sunscreens cause autism. She repeatedly talks about correlations as if they meant more than they do. The incidence of autism has risen in perfect correlation to the sales of organic food. She does not recommend more research to determine if organic food causes autism.

She worries about nanoparticles. She cites all kinds of laboratory evidence suggesting “possible” harm from nanoparticles, but no actual evidence of harm to humans from nanoparticles in sunscreens.

She is worried that sunscreens reduce levels of vitamin D, even though some research shows they don’t. She goes to great lengths to explain all of the possible harms from decreased vitamin D.

Coral reefs

She thinks it has been definitively established that sunscreen chemicals can result in coral death. She bases that opinion on lab studies and correlations (the tourism boom in Belize coincided with coral bleaching). A report by the Australian Government’s Great Barrier Reef Marine Park Authority doesn’t even mention sunscreens among the threats to the reef.

The ubiquity of sunscreen chemicals

She shows evidence that sunscreen chemicals are found not only in our water, but in household dust, breast milk, and pretty much everywhere. But in what amounts? The detection of minute amounts is a tribute to the incredible precision of modern laboratory methods, but it says nothing about whether those tiny amounts cause any significant harm to humans. Lab analysis can detect the tiniest amounts of all kinds of other chemicals. The human body is constantly coping with minuscule amounts of all those other chemicals, with no evidence of harm. We can’t avoid all of them, but we needn’t worry about all of them. The poison is in the dose.

Alternatives to sunscreens

She recommends “Mother Nature’s sunscreen:” an antioxidant UV protection diet that she says will strengthen the immune system and protect from cancer. She also recommends organic food, aloe vera, and a longlist of amino acids (including histidine, which she spells histadine) and other nutrients that are photoprotective, even caffeine and goji berries (juice found to reduce sunburn in mice). After sun exposure, she recommends putting olive oil and tea on the skin. Of course, there is no evidence that her “natural” measures are anywhere near as effective as sunscreens. She gives sensible advice about reducing sun exposure and wearing protective clothing. But she recommends avoiding all sunscreens because there is no sunscreen on the market that doesn’t contain harmful chemicals.

The precautionary principle

She says:

Indeed, studies examining sunscreens and their effectiveness or potential harmful consequences demonstrate conflicting results that researchers, themselves, state are difficult to explain. The major reasons for these inconsistencies are due to the fact that the human body and the interactions of the ecosystems are so complex it is difficult to design studies that can control all the individual and environmental variables in order to discern definitive answers.

She’s certainly right about that. But then she seems to assume that not knowing if there are harmful consequences equates to reasonable certainty that there probably are harmful consequences. And she is arguing that science can never rule out harmful consequences. Where does that leave us? She seems to think that if there is even a whisper of a suggestion of a possibility of harm, we should act to avoid that possibility. I disagree, because the precautionary principle fixates only on harms and disregards the benefits; and precautionary actions have often led to unforeseen consequences that were even worse.

Putting risks in perspective

Scott Gavura’s approach (see above) is much more reasonable. As a recent review concluded, “Given the established benefits of UV protection, the use of sunscreens remains an important part of an overall photoprotective strategy.”

Conclusion: Not good science

Plourde’s book is a cherry-picked, poorly reasoned diatribe, not a fair assessment of the scientific evidence. The bottom line: no, sunscreens don’t cause cancer; they protect against it. There are some legitimate concerns about possible adverse effects and environmental impacts, and we can continue to study possible risks and to look for newer, more effective, safer sunscreens. Meanwhile, we can continue to use existing UVA/UVB sunscreens judiciously, cover up, and avoid unnecessary sun exposure.