What are they?
Active ingredients in sunscreens are broadly divided into two categories: physical and chemical. Chemical sunscreens, which are soaked up by skin, can include one of over two dozen compounds—many of which are based on benzophenone. On a label, they’re listed as avobenzone, ecamsule (aka mexoryl) and oxybenzone, among others. They work by absorbing UV light. Physical sunscreens, in contrast, include components such as zinc oxide and titanium dioxide that sit on skin’s surface and reflect ultraviolet (UV) light away.
Should I be worried?
Many chemical sunscreen ingredients are endocrine disruptors. In 2010, Margret Schlumpf, an environmental developmental toxicologist from the University of Zurich, tested the breast milk of 53 mothers for environmental chemicals and found evidence of eight chemical sunscreen ingredients known for their endocrinal activity. In other studies, the compounds have shown up in blood and in urine.
To be considered a broad-spectrum formula, sunscreens must contain both UVA- and UVB-blockers. Physical sunscreens are often considered the “safer” of the two, although there is growing concern over the increasingly small size of the particles used (see “Nanoparticles” below). With no clear evidence linking chemical sunscreens to human development or health problems, the overall impact remains uncertain.
Bottom line: While the jury is still out on the long-term effects of these chemical ingredients, the link between sun damage and skin cancer is well-established—making sunscreen a pivotal tool to protect oneself from harmful UV rays.
What are they?
Nanoparticles are tiny materials that are thousands of times' smaller than the width of a human hair. Measured in nanometers, they can be synthetic or naturally-occurring, and are often used in cosmetic products.
Since the term “nanoparticles” refers to their size rather than physical or chemical characteristics, it can be difficult to define what a particular nanoparticle does. Nano-sized inorganic compounds, such as zinc oxide and titanium dioxide are the compounds most often used in sunscreens.
Should I be worried?
Due to their smaller size, nano-sized zinc oxide and titanium dioxide effectively absorb and reflect light. This makes them ideal sunscreen ingredients. Before the advent of nanoparticles, these same ingredients gave sunscreens a thick, white appearance, making them notoriously hard to rub in and cosmetically-inelegant. By shrinking the ingredient, a lighter, easier-wearing product was created.
It isn’t clear if nanoparticles cause any damage once absorbed; especially considering both already exist in our bodies. Zinc is an essential building block for good health while titanium is commonly used in medical and dental implants. “We just don’t know yet if there’s any long-term toxic consequence,” says Lisa DeLouise, an associate professor of dermatology and biomedical engineering and the lead author of a 2008 University of Rochester study.
The University of Rochester Medical Center showed these particles penetrating mice’s skin and accumulating in their hair follicles. A 2010 paper from Macquarie University in Australia showed a similar absorption of zinc oxide that appeared in urine and blood samples.
To see if your sunscreen contains nanoparticles of titanium dioxide or zinc oxide, check the label for either ingredient. Almost all sunscreens that contain either compound contain nanomaterials, particularly if the sunscreen goes on clear instead of white. But, as already mentioned, it’s important not to skip the sunscreen, as these compounds appear to be the safest ones on the market.
What is it?
Aluminium salts, including aluminum chlorhydrate and aluminum chloride, are active ingredients in many anti-perspirants that temporarily clog sweat ducts to keep sweat from escaping. Aluminum is not a normal component of biological tissue, so any traces of it in the human body originate from the outside.
Should I be worried?
Experiments by Philippa Darbre, the same researcher who works with parabens, suggest aluminum salts can penetrate the skin, showing up in breast tissue, breast milk, fluid from breast cysts and blood (though the studies couldn’t identify the source). And the salts may be able to penetrate shaved skin even more readily than unshaven skin, because razors make tiny abrasions in the skin— even when they don’t cause an obvious cut.
According to Darbre, aluminum may act as an endocrine disruptor by mimicking estrogen in the body, which in theory, could contribute to some types of breast cancer.
There is no clear link between the presence of aluminum in the body and breast cancer or any other illness. For every study that shows a potential relationship between aluminum and disease, there is another that shows none.
Keep in mind: While aluminum (and even parabens, phthalates, nanoparticles and chemical sunscreens) may not be hazardous on its own, consider the combined effect. Your paraben-containing shampoo may not be a big deal, but add in that birth control pill, the tofu you eat (that contains plant-based estrogens) and the BPA-containing bottle you still drink out of, not to mention canned foods and who knows what else, its effects are still murky. “What we really need is a better overview of all the chemicals in cosmetics,” says Darbre. “To draw accurate conclusions, we’ll need to look at the bigger picture, not just one individual chemical.”
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