Sunscreen Safety and Oxybenzone

Is oxybenzone in sunscreen safe? From Squintmom/Beautiful EntropyI love getting questions about science-related issues from readers. I particularly love it when a question intersects with an issue I myself am curious about, as happened when a reader got in touch with me last week:

I need some advice about sunscreen. I just read some articles on CNN about new FDA guidelines and the Environmental Working Group’s 2012 sunscreen review. Of particular concern is oxybenzone. The FDA claims it’s safe and very effective at protecting against UVA and UVB rays. However, the EWG says that oxybenzone is carcinogenic. Hmm… use sunscreen to prevent skin cancer, but sunscreen causes… skin cancer? That seems like a big time conundrum to me. The other thing I wonder about is who is the EWG? All I really know is they came up with the “Dirty Dozen” foods you should always buy organic. So what’s the deal? Should I toss all of last year’s sunscreen with oxybenzone and buy new? Is the EWG generally a trustworthy, “non-woo” authority?

The oxybenzone molecule

Let’s start with my professional opinions of the Food and Drug Administration (FDA) and of the Environmental Working Group (EWG). The FDA is routinely accused by consumer groups and conspiracy theorists of being “in bed with Big Pharma,” engaging in cover-up operations, putting profit ahead of consumer health, and so forth. I really don’t agree with this take on the organization, as I discuss in this post. The FDA’s history in the US is one of a largely appropriate trajectory. They’re a behemoth organization, and as such, they move slowly. They’re slow to approve new drugs because they insist on rigorous testing; this is one of the things that pisses off consumers who want to see new drugs come to market quickly. They’re relatively quick to warn consumers if there’s evidence that a pharmaceutical or substance is harmful, though they’re not alarmist and rarely respond to the results of an isolated study. The FDA is, to put it simply, stuck performing an impossible balancing act: they’re under public pressure to approve substances quickly, while they’re simultaneously under public pressure to keep anything that could potentially be harmful off the market. These missions are mutually exclusive, and I have to say that for the most part, the FDA handles their task as elegantly as a behemoth government organization can do. Have they made mistakes? Absolutely. But what I appreciate about the FDA is that they correct over time, such that their trajectory is generally appropriate and stable.

The EWG, on the other hand, is far more alarmist than the FDA. They’re not a government organization, but are rather a research and lobbying group made up of citizens and scientists. A survey of toxicologists (unaffiliated with the organizations about which they were questioned) revealed that most felt the EWG overstates risks associated with products. Specifically, toxicologists gave the EWG an accuracy score of 4.2 (1 = significantly understates risks, 3 = accurately states risks, 5 = significantly overstates risks). By comparison, the FDA got a 3 from the toxicologists, indicating that they felt the organization was accurate in assessing and reporting risks. For those who are curious, the U.S. Centers for Disease Control and Prevention (CDC) and the American Medical Association (AMA) also scored near 3, reflecting accurate portrayal of risks, while Greenpeace got a 4.5 — the highest score given — for significant overstating of risks. The Pharmaceutical Research and Manufacturers of America (PhRMA), on the other hand, scored a 2.3 for being the most significant understater of risks. Note that PhRMA is not a government organization, and is not tied to the FDA, the CDC, or other government health regulators.

As far as the EWG goes, I think they have their place. They report on research, but often issue warnings on the basis of single studies or studies with limited applicability. Case in point, they warn consumers against sunscreen containing retinyl palmitate (vitamin A) on the basis of a 2009 study that looked at mice rubbed with the chemical and exposed to light. The vitamin A mice developed more tumors, leading the EWG to report a link between retinyl palmitate in sunscreen and cancer. However, there are significant issues that limit the study’s applicability. Most notably, sunscreen only ever contains a small amount of retinyl palmitate. Dose is very important in toxicology; any substance — even water — is toxic in sufficient quantity. As such, a pure retinyl palmitate rub applied to mice doesn’t provide information about the toxicity of small amounts of the compound in sunscreen. In the end, groups like the EWG help to promote research on issues pertaining to toxicology and public safety, but speaking for myself, I look for corroborating research or concern from more moderate institutions before acting on an EWG warning. In response to the question from the start of this post, I think we can safely say that the EWG is “non-woo,” but they are a little jumpy.

On to sunscreen safety. First and foremost, there’s a major risk-to-benefit analysis that one must conduct when determining whether to use sunscreen and what type to use. This is because the sun emits ultraviolet radiation (UV) that damages cells, leading to development of wrinkles, aging of tissues, and skin cancer. Sunburns are an indication of particularly severe cellular damage — just one or two sunburns before the age of 18 significantly increases risk of skin cancer later in life — but even a so-called “healthy” tan is a sign that damage has occurred. Sunscreen is a part of protecting the skin from sun damage, but it’s not the entire equation. In fact, staying out of the sun during intense radiation hours (midday) and using physical protection such as clothing, sunglasses, and hats provides the best protection from harmful UV radiation. No sunscreen provides complete protection. To this end, one of the new FDA regulations regarding sunscreen labeling is that sunscreens will no longer be allowed to refer to themselves as “sunblock,” on the grounds that this inappropriately overstates protection. While there’s been some muttering by the EWG and other groups about whether sunscreen truly helps to prevent skin cancer, these concerns are largely based upon use of sunscreens that protect from only one type of UV radiation (broad-spectrum sunscreens are best, but not all sunscreens are broad-spectrum) and inappropriate use of or reliance on sunscreen. The general consensus among medical and government organizations, including the CDC and the AMA, is that sunscreen is an important component of safe-sun behavior.

The active ingredients of a barrier sunscreen.

There are two major classes of sunscreens: barrier sunscreens containing minerals (like zinc oxide and titanium dioxide) that reflect light, and chemical sunscreens that absorb the light and prevent it from penetrating cells. There is essentially no risk of absorbing the barrier compounds through the skin, leading even the EWG to note that these sunscreens are likely the safest and most effective. In times past, barrier sunscreens were unpopular because they had a greasy white appearance on the skin (remember Zinka from the 80s?). Newer technology allows for smaller particles (nanoparticles) of barrier compounds, which are less visible on the skin, though some formulations may still be greasy. There’s also some question as to whether these nanoparticle formulations appropriately protect from UVA, one of the types of UV (UVB is the other type). Unfortunately, while the sunlight reaching Earth is made up of mostly UVA, the SPF rating on sunscreen applies to UVB protection only. The new FDA regulations propose a set of standards for reporting UVA protection, as UVA exposure also leads to skin cancer. With regard to barrier sunscreens, then, the most effective UV protection comes from the old-school stuff: greasy, white, and slathered on thick. The next most effective UV protection comes from a nanoparticle formulation combined with a chemical sunscreen containing oxybenzone or similar for enhanced UVA protection. Of course, protection from UV is only part of the equation when it comes to assessing sunscreen safety; the other part is the safety of the sunscreen ingredients themselves.

The active ingredients of a chemical sunscreen.

Oxybenzone is currently raising hackles at the EWG, and is one of the reasons that their Sunscreens 2012 report contains so few “approved” choices. The compound occurs in nature — it’s in flower pigments — and is incredibly common in personal care products. It’s not only a sunscreen, it’s also a fragrance enhancer, preservative, flavor enhancer, and so on. The CDC reports that a recent random sample of Americans revealed oxybenzone in 97% of urine samples (Calafat et al). However, the significance of this information has not yet been determined. The EWG calls oxybenzone a “potential hormone disruptor,” citing the European Commission on Endocrine Disruption (pdf) (ECED), which basically means that the EWG is saying they don’t like oxybenzone on the grounds that the ECED doesn’t like oxybenzone. As to why the ECED takes issue with it, they (like the EWG) are exceedingly cautious. The EWG cites two studies (Ma et al,* Ziolkowska et al) that show the potential for weak endocrine disruption. {Note that the Ma et al reference is incomplete on the EWG website, and I was able to find no evidence of it in the scientific literature}. The extent to which the results of these studies, conducted on cells with pure oxybenzone compound, are relevant to use of the compound in sunscreen are unknown. As the American Cancer Society points out:

Virtually all substances known to cause cancer in humans also cause cancer in lab animals. But the reverse is not always true – not every substance that causes cancer in lab animals causes cancer in people. There are different reasons for this.

First, most lab studies of potential carcinogens (cancer-causing substances) expose animals to doses that are much higher than common human exposures. This is so that cancer risk can be detected in relatively small groups of animals. But doses are very important when talking about toxicity. For example, taking a couple of aspirin may help with your headache, but taking a whole bottle could put you in serious trouble. It’s not always clear that the effects seen with very high doses of a substance would also be seen with much lower doses.

Second, there may be other differences between the way substances are tested in the lab and the way they would be used, such as the route of exposure. For example, applying a substance to the skin is likely to result in much less absorption of the substance into the body than would be seen if the same substance is swallowed, inhaled, or injected into the blood. The duration and dose of the exposure also help determine the degree of risk.

While the above refers to cancer risk, the same is true of other toxic effects of compounds that are revealed through laboratory and animal studies. With specific regard to cancer and oxybenzone, even the cautious EWG notes that there’s no evidence that oxybenzone is carcinogenic — or, more accurately, THERE IS evidence that oxybenzone IS NOT carcinogenic (non-mutagenic in 4 of 4 studies: CTFA, 1980; DHEW, 1978; Hill Top Research Labs, 1979; Litton Bioneics, 1979).

Taking all the information together and conducting a risk-to-benefit analysis, I think it’s fair to say that because of the limited data available and the availability of alternatives to oxybenzone, it may be worth avoiding it in sunscreen, but there’s no reason to get particularly excited about previous use or occasional future use. Given that it’s present in almost all chemical (non-barrier) sunscreens, this essentially leaves the barrier sunscreens containing zinc oxide and titanium dioxide. If one chooses to use the nanoparticle formulations with somewhat reduced UVA protection, one must then decide whether to use a chemical sunscreen for additional protection — but this once again leads to oxybenzone exposure.

One last thing: with regard to old sunscreen, if in doubt, throw it out. The CDC recommends that sunscreen be no more than three years old if there’s no expiration date on the bottle. If the bottle has an expiration date, abide by it. The protective chemicals in sunscreen break down over time, meaning that protection wanes.

Science Bottom Line:* Given that there is no sunscreen that provides complete protection, the evidence suggests that the safest choice (particularly for children) is the use of zinc oxide or titanium dioxide sunscreen (I prefer nanoparticle formulations for convenience and aesthetics), without a chemical sunscreen backup. This should be augmented through the judicious use of shade, clothing, sunglasses, and hats, particularly during the most intense periods of sunlight.


How do you protect your family’s skin outdoors?



Calafat et al. Concentrations of the sunscreen agent benzophenone-3 in residents of the United States: National Health and Nutrition Examination Survey 2003–2004. Environ Health Perspect. 2008 Jul;116(7):893-7.

Ziolkowska et al. Endocrine disruptors and rat adrenocortical function: studies on freshly dispersed and cultured cells. Int J Mol Med. 2006 Dec;18(6):1165-8.


Cell Phones and The Brain

Wireless telephones, including both cellular phones and cordless home phones, emit electromagnetic radiation in the radiofrequency range. It’s been suggested in recent years that using a wireless phone on a regular basis could expose the brain to large doses of radiofrequency radiation, the risks of which are currently unknown. Particularly because children have rapidly developing brains, could using cell phones or cordless home phones increase the risk of cancer or have other negative health effects?

Radio waves are a type of electromagnetic radiation, which (though the word “radiation” makes them sound scary and dangerous) are very low in energy. As such, they are incapable of doing the kind of damage that, say, x-rays and nuclear radiation can do, as explained in a previous article. However, while radio waves can’t break chemical bonds like certain other types of radiation can, they are nevertheless a type of energy. In fact, cell phone use has been shown to increase the temperature of the skin with which the phone is in contact by more than 2°C over a period of less than 10 minutes (see, for instance, Anderson et al, Straume et al), though very little of this increased temperature is likely due to the radiation itself. It’s also not likely that much of the heat actually makes it through the skull into the brain. Still, because little is known about the potential effects of routine exposure of the brain to radiofrequency radiation, scientists continue to investigate the safety of wireless phones and similar devices.

Radiofrequency energy isn’t very penetrating; it’s absorbed by the head and hand of a cell phone user, but it can’t travel very far into the head. Therefore, if cell phones increase the risk of tumors, the tumors should appear in the regions of the brain nearest the ear. A recently published study with a very large number of participants (more than 350,000) examined the relationship between brain tumors and cell phone use. The authors found no correlation whatsoever, leading them to conclude that cell phone use does not increase the risk of brain tumors (Frei et al).

An even more recent study found, however, that cell phone use does alter the metabolism of glucose in the brain; specifically, using a cell phone increases the extent to which the regions of the brain nearest the phone antenna burn sugar (Volkow et al). Increased glucose metabolism (burning of sugar) is a sign that cells are working harder, so the results of this study suggest that cell phone use alters the operation of brain cells. The authors did not attempt to discern, nor did they propose, a mechanism for this effect. It remains to be determined why radiofrequency radiation would increase brain cell activity, and what ultimate effects that increased activity might have. An animal study, however, suggests that radiofrequency might change certain functional parameters of brain cells (how easily excited they are, for instance), and might alter the release of neurotransmitters, which are brain cell communication molecules (Hyland). The potential involvement of neurotransmitters is a particularly distressing possibility where it comes to a child’s brain, which is still developing and which is quite sensitive to neurotransmitter concentrations (though it’s worth bearing in mind that, as of yet, the involvement of neurotransmitters is purely hypothetical).


Science Bottom Line:* There’s no evidence that cell phones cause cancer, but there is evidence that they affect brain activity, and there’s not much yet known about how they do so, or what the long-term effects might be. A reasonable course of action in situations like this, in which the risks are poorly defined, is to proceed with caution. Using a cell phone for short periods during the day and/or infrequently for longer periods isn’t likely to be a problem, but you may wish to invest in a headset if you (or your child) uses a cell phone frequently or for long periods of time on a regular basis.


Do you worry about the long-term health effects of cell phone use?



Anderson et al. Measurements of skin surface temperature during mobile phone use. Bioelectromagnetics. 2007 Feb;28(2):159-62.

Frei et al. Use of mobile phones and risk of brain tumours: update of Danish cohort study. BMJ. 2011 Oct 19;343:d6387. doi: 10.1136/bmj.d6387.

Hyland, G. Physics and biology of mobile telephony. Lancet. 2000 Nov 25;356(9244):1833-6.

Straume et al. Skin temperature increase caused by a mobile phone: a methodological infrared camera study. Bioelectromagnetics. 2005 Sep;26(6):510-9.

Volkow et al. Effects of cell phone radiofrequency signal exposure on brain glucose metabolism. JAMA. 2011 Feb 23;305(8):808-13.

Glowing Green Milk

Mammograms aren’t fun for a variety of reasons. Perhaps the most obvious is that they involve smashing the breasts between two plates so that they resemble — as much as is possible for semi-spherical body parts — pancakes. I have a mammogram coming up shortly, and to be honest, I’m less concerned about the former, and am more bothered by the fact that I’m old enough to be on my second mammogram. Apparently, however, doctors don’t like it when mammograms converge with lactation in space-time. For instance, the health provider who prescribed my upcoming mammogram told me, “You may want to pump and dump afterward, because of the radiation.” When I actually called to schedule the procedure, I was told that they would be doing an ultrasound instead, because I was lactating and they didn’t want to “expose my milk to the radiation.”

Now, I teach chemistry, so I’m well aware of how common are fears and misconceptions about radiation. I have to admit, however, that I didn’t think doctors’ offices would share (or propagate) those fears and misconceptions. In any case, I thought it would be worth addressing why mammograms (and MRIs, and x-rays) won’t make your milk glow green (as cool as that would be), and why you don’t need to pump and dump if you have to have one of these procedures. (Incidentally, Kellymom has lots of information on what is and what is not safe during lactation.)

We tend to think of anything called “radiation” as being bad, and generally associate exposure to radiation with things like cancer, Chernobyl, and Spiderman. Thankfully, most radiation can’t produce cancer, and unfortunately, no radiation has the ability to produce Spiderman. “Radiation” is really just a term for radiant energy, which is even more technically referred to as electromagnetic radiation, or EMR. EMR encompasses many different types of phenomena that we don’t necessarily think of as related to one another. These include — but are not limited to — x-rays, visible light, and radio waves. Without getting too deep into the physics, all EMR has a frequency, and the frequency of the EMR determines the type of radiation. It’s possible to draw a limited analogy to sound here; the pitch of a sound is a function of its frequency, so frequency determines the “type” of sound. The analogy between sound and EMR doesn’t take us far, however, and the important point here is that high-frequency EMR has high energy.

From Wikipedia, Philip Ronan

The reason all this matters is that some EMR can interact with molecules, and the way EMR interacts with a molecule depends upon the type of EMR. Think of a molecule as being made up of particles (called atoms) connected by springs (bonds). The springs (bonds) naturally bend and stretch, and very high energy EMR can “overstretch” the springs and make them break, like this:

From Hendrickson, K. "Chemistry In The World" 2010.


Break the bonds, and you destroy the function of the molecule. If the molecule that gets broken is, say, DNA — your genetic material — then bad things happen, including disease, cancer, aging, and so forth. The only types of EMR with enough energy to break bonds in molecules are UV light, x-rays, and gamma rays (collectively called “ionizing radiation”). These are the only types of EMR that, consequently, can cause cancer and so forth (note that despite their bad reputation in some circles, microwaves have completely insufficient energy to cause cancer). Ok, so x-rays can cause cancer, as can mammograms (which rely upon x-rays). MRIs can’t, since they don’t use ionizing radiation, and rely instead upon the behavior of atoms in a magnetic field.

If x-rays fall into the category of ionizing radiation, why shouldn’t we worry about the milk that gets shot full of x-rays? The answer to this is simply that very, VERY few phenomena can actually make things radioactive. X-rays, and even gamma rays (which come from nuclear reactions and can cause a variety of cancers, radiation poisoning, and so forth) can’t make the things exposed to them radioactive. If you were exposed to nuclear fallout (like from the Chernobyl disaster), you could temporarily “become radioactive,” but only because nuclear fallout includes bombardment with subatomic particles called neutrons (among other things). If you have certain types of radioactive material introduced into your body, you can emit radiation due to the presence of the radioactive material. However, it is impossible for you (or your fluids) to become radioactive as a result of x-ray exposure. The only thing the x-rays could theoretically do to your milk would be to break down some of the proteins and other molecules (though they’re unlikely to, because the dose is so small), and furthermore, this wouldn’t affect the quality — or the safety — of the milk.

I Googled lactation and mammography, because I wanted to know what it was (assuming most medical professionals know there’s no risk of radioactive milk from a mammogram) that would cause a health practitioner to put off a mammogram on a lactating woman (which, according to Google, happens quite often). It turns out that practitioners worry about the “goo-factor.” Breast milk is a bodily fluid, and apparently the staff of imaging clinics is concerned that it will, well, squirt on things. Not that it does, generally speaking…but regardless, this appears to be a major motivating factor with regard to lactating women and the medical profession’s desire to keep them, and their squirting milk, away from those hard-to-clean mammography machines.


Science Bottom Line:* There is no danger to your milk if you have to have a mammogram or x-ray while you’re lactating. There is, as always, some danger to you personally any time you’re exposed to ionizing radiation, which is why it’s always important to weigh the risks against the benefits when you need to have imaging done. You don’t need to pump and dump unless you’re engorged.


What medical procedures have you wondered (or worried) about during lactation?