Sunscreen Chemophobia: Oxybenzone

(I wrote this for participation in the 2012 'Toxic Chemicals' Blog Carnival, over at ScienceGeist)

This 'suit' wants to sneak more chemicals into your sunscreen!
Source: EWG 'Hall of Shame'

Courtesy of Mother Jones and the Environmental Working Group (EWG), we can all breathe a bit easier. The eco-conscious nonprofit organizations have just released their recommendations for summer sunscreens. Unsurprisingly, the Top 20 are cut from the same cloth; words such as "natural," "clear," "garden," and "organic" abound. Ingredients, too: ~20% or so of 'micronized' (>100 nm) zinc oxide, some titanium dioxide for good measure . . .and just about every fruit oil, tea extract, or skin moisturizer you can think of.

Actually, I found myself much more drawn to the 'Hall of Shame.' These sunscreen outlaws represent all the nefarious tricks #BigChem might play on an unsuspecting public - sneaking in oxybenzone, "nano-zinc," and retinyl palmitate (synthetic Vitamin A) to make a buck off naive customers. I won't weigh in on the last two ingredients, but oxybenzone certainly caught my eye.

Oxybenzone, also called benzophenone-3, finds its way into sunscreen, lipstick, lotions, paints, and polymers. According to the Merck Index, it was first prepared over a century ago (1906), and patents from the 1950s show a simple one-step prep, Friedel-Crafts acylation of benzoyl chloride, which forms the new C-C bond between the "left" aromatic ring and the C=O group. Oxybenzone actually absorbs UV light over a wide swath of the spectrum, from 280-320 nm, meaning it offers sun protection from both UV-A and UV-B.

oxybenzone

The EWG calls oxybenzone a "hormone-disrupting chemical." Like bisphenol A (BPA), another well-reported and contentious molecule, oxybenzone contains a free phenol group, and two aromatic rings linked by a central carbon bridge. These atomic features tend to crop up in compounds that mimic estrogens in the body.

Well, does oxybenzone pose endocrine risks? Where could you find that info, anyway?

I started where I usually do: TOXNET, the U.S. National Library of Medicine reference database. Oxybenzone triggers six references from the Developmental Toxin (DART) literature, which cover 18 years of studies on fish, mice, and cell cultures. I also checked PubMed, grabbed a 1992 National Toxicology Program (NTP) oxybenzone report, and the 2008 European Commission SCCP recommendations for consumer exposure.

What do the data show? At the highest doses - 50,000 ppm - all animals develop liver, kidney, and reproductive organ damage. But the dose makes the poison, and as you feed (oral) or rub on (dermal) less compound, the side effects fall off rapidly. No teratogenicity (fetal harm), no mutagenicity (DNA errors), and no unexplained deaths. The scientists did observe indications of "moderate reproductive toxicity," but, again, these showed up in the highest-dose groups. To replicate these effects in humans, you'd have to literally eat spoonfuls of the compound (For ongoing oxybenzone studies, see: NTP, CDC).

The European Union, exemplars for cautious chemical regulation, provide a convenient calculation for human exposure: for a standard 60 kg (132 lb) person, given skin absorption, sunscreen concentration (6% oxybenzone), and average application at 18 g (just over half an ounce), exposure = 1.78 mg / kg / body weight / day. That's ~2 ppm, fully 500 times less than the lowest doses currently testing at the NTP (see above). The 2008 EU panel assigns oxybenzone a Margin of Safety of 112; compounds above 100 generally meet their benchmark for safe use.

Delicious cup of low-dose,
 bioactive compounds
Source: Green Tea Health

But, hormones influence body chemistry at miniscule doses, right? And, these sunscreen compounds are ubiquitous! How can we be absolutely certain that they aren't toxic? Well, I'll counter with a simple observation: herbal, plant, and seed extracts - like the shea butter, aloe juice, camellia seed oil, jojoba, calendula, papaya, plantain leaf, starflower seed, linseed oil, green tea extract, olive oil, plankton, avocado oil, primrose oil, and bark extracts found in the "alternative" sunscreens - have just as many, if not more bioactive compounds!

For chemophobic consumers, the general (albeit, flawed) reasoning seems to go something like this:

Many small, aromatic, heteroatom-containing molecules may be endocrine disruptors.
Industrial companies produce many such chemical compounds.
Therefore, many "industrial" chemicals cause health problems.

Magically, however, this logical logjam clears if you mention "natural," "organic," or "chemical-free" formulations. I suspect the reasoning goes:

Many small, aromatic, heteroatom-containing molecules may be endocrine disruptors.
Natural product extracts contain dozens of compounds, some unknown, many untested.
But, since they're from plant extracts, they're probably safe.

Would consumer impressions of oxybenzone change if it were. . .a natural plant extract? Good news: it is.

That's right, the compound occurs naturally in various flower pigments, which chemically trained eyes might have detected in the "resorcinol-like" framework. To stretch the metaphor, given the eased FDA rules regarding dietary supplements, I wonder if one could employ this tactic to produce a "natural, plant-based sunscreen" that still contains oxybenzone!

Happy summer, everyone! Think clearly, ask questions, and challenge assumptions. And, wherever you buy it from, remember to always wear your sunscreen.

For a different perspective on EWG's sunscreen data, head over to Science-Based Medicine