Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: jamanetwork.com/journals/jama/… PART-2 of a study on chemical sunscreen absorbing into the blood. This is surely going to stir up more controversy. Let me break it down in this thread #tweetorial 👇🏾
In May 2019 the same group of investigators published a study in @JAMA_current asking the question: What is the concentration of chemical sunscreen that gets in the blood if used under maximal conditions (i.e. Used 4 times per day for 4 days)? Study here: jamanetwork.com/journals/jama/…
I did a #tweetorial last year on the original study and explained the history of the controversy of sunscreen safety in general:
How is this new study different?
The new study is different in 2 main ways:
1)The investigators wanted to know the plasma concentration of sunscreen after just ONE application.
2)The investigators wanted to know how long chemical sunscreen stayed in the blood in the weeks after maximal application.
1)The investigators wanted to know the plasma concentration of sunscreen after just ONE application.
2)The investigators wanted to know how long chemical sunscreen stayed in the blood in the weeks after maximal application.
For #1 they found that all 6 sunscreen filters tested achieved plasma concentrations significantly above the FDA threshold after a SINGLE application.
For #2 all products tested remained above the FDA threshold at day 7, and for homosalate and oxybenzone they remained above the threshold on day 21. The half-life of these filters after maximal use ranged between 27 hours and 157 hours (that’s 6.5 days!)
The authors also did something else interesting; they did tape stripping of the skin on days 7 and 14 which showed persistence of sunscreen filters, raising the possibility that the skin could serve as a depot for ongoing absorption after daily sunscreen application is stopped.
The findings are may be frightening to some people, but I want to EMPHASIZE that they do NOT prove sunscreen is harmful to human health. The study only shows that chemical filters are absorbed (which we’ve known for many years) and health consequences are unknown.
So far, there has been no credible evidence that the use of chemical sunscreen is harmful to human health, rather we know UV protection has benefits in preventing skin cancer in certain groups, along with other benefits like less sun burns, less wrinkles, etc.
Keep in mind, this clinical trial was performed in the dead of winter and participants had limited sun exposure, so the kinetics of absorption may be different than in real world use.
Remember, most people don't regularly put on sunscreen on 75% of their body for multiple days straight!
Where do we go from here? I think we need to conduct further safety studies on the consequences of chemical sunscreen absorption into the blood. This is particularly important in children.
For now, you shouldn’t abandon sunscreen use, which is part of UV safety, which includes photoprotective clothing, eyewear, and avoidance of intense sun exposure.
Remember the use of mineral-based sunscreen (ingredients: zinc oxide and titanium dioxide) is a well-established safe alternative.
I want to thank @KanadeShinkai for inviting me to co-author the editorial in @JAMA_current, take a look for more on the interesting study by Matta et al: jamanetwork.com/journals/jama/… 
Does this new study scare you about using sunscreen?
Based on this study will you change what type of sunscreen you use (mineral/physical vs chemical)?
