COMMENTARY

Is the Sunscreen Scare Legitimate?

How Does It Compare With Caffeine From Coffee, or Nicotine From Cigarettes?

F. Perry Wilson, MD, MSCE

Disclosures

May 21, 2019

"Be nice. Wear your sunscreen. I love you."

I uttered this mantra every day as my kids were whisked off to day camp last summer, cognizant of the burns I suffered as a free-wheeling and UV-exposed youth. I knew there was ample biological evidence that sunscreen, by preventing severe burns, would reduce their risk for skin cancer in the future. This is #GoodParenting.

And then I came across a recent article in JAMA[1] that kicked the parental guilt into high gear. The study showed that the active ingredients in many chemical sunscreens had significant systemic absorption. And the truth is, we have no idea if that matters.

Why was this study done now?

Sunscreens are treated as over-the-counter medicines in the United States, but they were put on the market before the modern era of oversight by the US Food and Drug Administration (FDA), meaning the FDA had not (yet) evaluated their potential toxicity. Then last year, the FDA created a guidance document with a specific suggestion: If any of the active ingredients in sunscreen achieve a steady-state blood level of greater than 0.5 ng/mL, formal toxicology studies should be performed.

That 0.5 ng/mL level is not arbitrary. It's the same level that the FDA uses to determine whether impurities introduced in drug manufacturing need to be evaluated for toxicity. It's the "OK, do we need to worry about this?" level.

The FDA researchers conducted a formal pharmacokinetic study with 24 healthy volunteers who were cooped up (indoors, without sunlight) for a week. According to manufacturer instructions, sunscreen was applied four times a day for the first 4 days, mimicking what you might do on a typical vacation somewhere sunny. Throughout their stay, their blood was tested for levels of avobenzone, oxybenzone, octocrylene, and ecamsule (the most common active ingredients).

All four chemicals achieved blood levels higher than that 0.5 ng/mL threshold. In fact, with the exception of ecamsule, they blew right through it. The average peak oxybenzone level was around 200 ng/mL—that's 400 times higher than the level to trigger a formal toxicology review.

This study was preliminary, but if you look at the drug concentration curves, you can make a couple of inferences. First, the average drug level increased each day during the 4 days that sunscreen was applied. This means that there is drug accumulation (at least when you are applying it four times a day).

You can also see that drug washout was rather slow. Although the authors don't provide the specific numbers, the half-life of the drug appears to be on the order of a few days—meaning that over a summer of use, this could really add up.

More formal, longer-term studies are needed, and the FDA has stated that it has asked industry and "other interested parties" to conduct them. Sunscreens will stay on the market for now.

And that's fine. Thinking about it, is it any surprise that these chemicals are absorbed? A quick glance at their chemical structures show interconnected benzene rings that just scream "fat-soluble."

But just because something gets into your body doesn't mean it's bad for you. I know these compounds have chemical names, but the assumption that artificial compounds are worse for you than all of the other stuff we put in our bodies is known as the "naturalistic fallacy." By way of comparison, the average blood level of caffeine after a cup of coffee is 50 times higher than the peak concentration of oxybenzone seen in this study. But that oxybenzone level is about seven times higher than the blood nicotine level seen after smoking a cigarette.

In other words, the fact that you can measure something in the blood doesn't tell you anything about whether it is bad for you. We simply don't know what the risk is. And we need to find out.

Personally, I wouldn't call for a freeze on chemical sunscreens. These drugs have been used for decades and there have been no strong epidemiologic signals of harm. Quite the opposite, they have probably prevented uncounted cases of skin cancer.

The problem with studies like these is that the fear they engender may do more harm than the good science that results from them. Nothing has changed about the harm of UV rays since the publication of this study in JAMA; you still don't want your skin exposed to them.

But it may be worth remembering that chemical sunscreens are not the only option. Clothing and hats provide excellent sun protection, and the systemic absorption of a sombrero is pretty low. And, of course, there are barrier sunscreens (formulated with zinc and titanium dioxide) which, yes, leave you looking like an 18th century consumptive, but which are generally regarded as safe.

This summer, my mantra may change a bit: "Be nice. Wear your embarrassingly white sunscreen. I love you."

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