The great sunscreen ingredient debate

In a commentary issued on May 6, the Food and Drug Administration stated that “with sunscreens now being used with greater frequency, in larger amounts, and by broader populations, it is more important than ever to ensure that sunscreens are safe and effective for daily, lifelong use.” The statement coincided with the publication of the randomized study, “Effect of sunscreen application under maximal use conditions on plasma concentrations of sunscreen active ingredients,” by Matta et al. of the FDA and others in JAMA (2019 May 6. doi: 10.1001/jama.2019.5586). A maximal usage trial examines the systemic absorption of a topical drug when used according to the guidelines given for the product’s maximum usage. In this study, adult participants were randomized to one of four commercially available sunscreen products: spray 1 (n = 6), spray 2 (n = 6), a lotion (n = 6), and a cream (n = 6). Two mg of sunscreen per 1 cm² was applied to 75% of body surface area four times per day for 4 days, and blood samples were collected from each individual over 7 days.

Dr. Naissan O. Wesley

Plasma concentrations of the four active ingredients tested – avobenzone, oxybenzone, octocrylene, and ecamsule – were above 0.5 ng/mL. The FDA’s guidance for industry and proposed rule on OTC sunscreens state that active ingredients with systemic absorption at 0.5 ng/mL or higher or with possible safety concerns need to undergo further nonclinical toxicology assessment to evaluate risk of systemic carcinogenicity, developmental/reproductive abnormalities, or other adverse effects.

Absorption of some sunscreen ingredients has been detected in other studies. Despite systemic absorption, two active ingredients – zinc oxide and titanium dioxide – have been found by the FDA to be generally recognized as safe and effective. But for 12 other active ingredients (cinoxate, dioxybenzone, ensulizole, homosalate, meradimate, octinoxate, octisalate, octocrylene, padimate O, sulisobenzone, oxybenzone, and avobenzone), there are insufficient data to make a “generally recognized as safe and effective” determination; thus, more data have been requested from the manufacturers. While physical blocking sunscreens have improved in their UV-blocking ability without compromising cosmesis over the past several years, some sunscreens containing chemical blockers are able to achieve higher SPFs with good cosmesis when applied to the skin.

Our skin acts as the ultimate barrier between ourselves and the environment, and it is not uncommon for substances to be blocked, absorbed, or excreted from the skin. Absorption of an ingredient through the skin and into the body does not indicate that the ingredient is unsafe. Rather, findings such as these call for further testing and research to determine the safety of that ingredient with repeated use. Per the FDA, such testing is part of the standard premarket safety evaluation of most chronically administered drugs with appreciable systemic absorption.

In February 2019, the FDA’s proposed rule was issued to “update regulatory requirements for most sunscreen products in the United States,” with the goal of bringing OTC sunscreens “up to date with the latest scientific standards,” according to the FDA May 6 commentary. “As part of this rule, the FDA is asking industry and other interested parties for additional safety data on the 12 active sunscreen ingredients currently available in marketed products” mentioned previously. These rules are being put into place to address the “key data gap” for these 12 ingredients, which is “understanding whether, and to what extent the ingredient is absorbed into the body after topical application.”