Homemade Sunscreens – Yea or Nay?
Posted on Wednesday, May 29th, 2019
Did you see the piece that PBS NewsHour recently ran on the dangers of DIY sunscreens?
No sooner did they did cite an FDA-led JAMA study published this past May on the potential absorption of sunscreen ingredients than they downplayed its significance. The study was small, they said – which it was (though it actually included 24 participants, not the 10 they reported, 23 of whom completed the trial) – and it didn’t find that the ingredients were harmful (because that wasn’t the point of the study).
What did the study show? As MDLinx nicely summarized,
The researchers asked 24 adults to apply sunscreens with one of four key ingredients at the recommended amount (2 mg/1 cm2 applied to 75% body surface area) four times daily for 4 days; 30 blood samples were collected over 7 days from each participant. While this application amount might seem like a lot, it’s roughly equivalent to that which a diligent tourist would use over a week-long visit at a tropical resort.
According to the daily blood tests, concentrations in the bloodstream of all four ingredients increased daily through day 4, and had a continued presence after disuse, pointing to an extended half-life. Overall, the investigators found that the active sunscreen ingredients were absorbed into the blood stream at levels that—within days—reached > 0.5 ng/mL, the threshold at which they should trigger FDA requirements for safety studies of systemic carcinogenicity as well as developmental and reproductive effects.
And that brings us to another item from the FDA which didn’t apparently make it into the PBS report.
This memo, distributed back in February, outlines a proposed rule change that would, among other things, classify 12 of 16 active ingredients commonly used in sunscreen as no longer “generally recognized as safe and effective.” Why? Because no one actually knows if they’re in fact safe or not.
Hence, the quest for alternatives – for product made with materials that are known to be safe.
But the PBS piece does ultimately make a valid point: While recipes you find online may sound good, putting together a formulation that works well is a little tricker than it sounds. As EWG has noted,
To be effective, mineral sunscreens need ingredients that hold zinc oxide or titanium dioxide in a suspension to provide an even coating on the skin. Without careful formulation, the mineral ingredients can settle or clump, leaving gaps in skin coverage.
On her blog, Realize Beauty, professional cosmetic chemist Amanda Foxon-Hill describes how she made batches of sunscreen with zinc oxide, shea butter and other ingredients, and then had them tested at a lab. The mixtures she thought would come out at SPF 30 ended up at SPF 12. The one she thought would be SPF 35 came out at SPF 8.
“Epic failures all,” she wrote, “and what was worse was that this was all my own work.”
“Even a change in fragrance,” Foxon-Hill notes in an update to her original post, “can affect SPF.”
Also of concern is that many recipes specify the use of nano zinc or titanium, and, as the NIH so plainly puts it, “Very little is known about the potential human health effects of nanoparticles.” Inhaling them can be risky.
Instead, the better option may be to use something like EWG’s Guide to Sunscreens to find the safest options for your needs – and also to keep in mind that sunscreen is just one tool for making sure you don’t get overexposed to UV rays while you’re out and about. EWG offers some good tips on this matter, as well, so check them out…and have fun in the sun this summer!