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Does your system absorb sunscreen ingredients?

March 14, 2020 / Duncan Fisher
A new study says yes, but not to worry too much

Your correspondent was talking over summer plans with colleagues recently, when an interesting topic came up. Wasn’t it true, came the question, that your body can absorb some of the ingredients in commercial sunscreens? And isn’t this bad?

It just happens that there’s research on that, and some of it is very recent – the most recent of it published a mere two months ago, in January, in the Journal of the American Medical Association.1

We know from studies prior to this one that, yes, there is some bodily absorption of 4 ingredients that are active in well-known sunscreens. They’ve been studied because these things are watched by the US Food and Drug Administration. For sunscreen ingredients they monitor the time it takes for systemic exposure to exceed 0.5 nanograms/millilitre. This is spoken of as a ‘pharmacokinetic’ measure, a benchmark for how much and how fast a compound works inside an organism.

The idea with this study, engagingly named ‘Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial,’ was to assess absorption and pharmacokinetics of 6 active ingredients, under conditions simulating normal and extreme use. These were avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate.

48 healthy participants in sunny West Bend, Wisconsin, were randomized to put on screening lotions, aerosol sprays, non-aerosol sprays, or pump sprays. Coverage was standardized to 2 milligrams per square centimetre over 75% of the body surface, and applications were repeated at specified intervals. Blood samples were taken, to see how much of these compounds, if any, got through the skin.

Mean plasma concentrations of all 6 ingredients exceeded 0.5 ng/mL on day 1, after a single application. By study’s end they exceeded by quite a lot.

For avobenzone, the maximum concentrations were 7.1 ng/mL for lotion, and around 3.5 ng/mL for the sprays.

Oxybenzone concentrations were 258.1 ng/mL for lotion and 180.1 for aerosol spray.

The other products yielded numbers that were between these. The pattern with all of them was that absorption was highest with lotions.

So what does this mean? Is it bad?

Not by itself. That FDA benchmark is merely the threshold for considering waiving some of the usual, additional safety studies that are used in approving sunscreens. It’s pretty conservative, and it’s largely arbitrary. Moreover, this study was what’s spoken of as an exploratory maximal usage trial; doses far exceeded what’s likely to be used by an average sunbather at the beach.

These numbers don’t actually mean that people should not use sunscreens containing these ingredients.

Are the ingredients – let’s say they’re used in really, really high concentration – are they themselves unsafe? The FDA is working on that. At customary usage levels the answer is no. But they’re looking closer, and they’re expanding to 12 the list of sunscreen ingredients they want to know more about.

In the meantime, should you continue to use sunscreens? Absolutely. Yes, you should. On this, even cautious regulatory agencies are unanimous. (Also wear your hat and stay under your beach umbrella.)

And while we wait, are there any sunscreen ingredients that are known already to be safe? Yes. There are two. They are zinc oxide and titanium dioxide. They don’t absorb at all.

The American Academy of Dermatology says that if you’re worried, or you just want to wait for the new data, use these in the meantime.

As for that new data, we'll let you know when it comes.

1Matta MK, et al. JAMA. 2020 Jan 21;323(3):256.

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