About the author: Dr. Aghajan earned her M.D. from UC San Diego, where she also completed her internship in Internal Medicine. She is now a neurology resident physician at Harvard. Her interests include preventative medicine and brain health, specifically reducing the risks of cardiovascular and cerebrovascular diseases. She spent the last eight years in sunny San Diego raising her small family in a city where the sun shines year-round and sunscreen is of utmost importance!
There are two categories of sunscreen ingredients; organic and inorganic filters. Organic filters are aromatic compounds that absorb UV radiation and convert it to small amounts of heat. Oxybenzone is the most commonly used organic UVA filter worldwide. Ozybenzone has recently come under investigation by the FDA and other organizations to evaluate its safety. Recently the FDA sponsored a randomized study to determine the systemic exposure of oxybenzone and other organic filters in commercially available sunscreen products (spray, lotion, or cream). In this study, volunteers applied sunscreen four times a day for four days and had their blood sampled to measure the amount of chemical. The results showed exposures exceeding 0.5 ng/mL, which is the threshold established by the FDA for toxicology for sunscreens (1). Based on this, while the FDA has not banned the sunscreen, it has recommended further safety testing. Another larger trial looked at oxybenzone blood levels after application of available commercial sunscreen across 48 healthy volunteers, and showed that even after a single application blood levels were still greater than 0.5ng/ml. The ingredients remained detectable in the skin up to day 14 (2). The CDC collected exposure data in American children and found that adolescent boys with higher oxybenzone levels had significantly lower total testosterone levels (3). Large organizations recommend continuing to use sunscreen but warn that the scientific community does not know the full extent of potential harms or safe levels until further research is done. For now, these commercial sunscreens are still available to purchase on the market. For people concerned about systemic absorption, potential toxicities and hormonal effects of sunscreen containing Oxybenzone, consider using alternative sunscreen with inorganic (mineral) ingredients.
Another reason to avoid Oxybenzone is that it’s the most frequent cause of sunscreen-induced allergic contact dermatitis (4). Although this side effect is rare, people with sensitive skin or allergic reactions may want to steer clear of this ingredient.
Oxybenzone has been shown to have estrogenic effects in animal studies. In one study, oxybenzone caused increase growth of the uterus in rats (5). In humans, little is known about the long-term effects of oxybenzone on hormones, puberty, or fertility. In a study of 501 couples trying to get pregnant, the male partners’ urine concentration of organic sunscreens was associated with a longer time to pregnancy (6).
The other form of sunscreen is composed of inorganic filters, which are mineral compounds such as zinc oxide or titanium dioxide that reflect and scatter vs. absorb UV light. In contrast to organic sunscreens, inorganic sunscreens have less irritation and sensitizing potential. They offer broad spectrum protection against UVA and UVB. In the past, inorganic sunscreens had large particles that formed a white film on the skin. To overcome this cosmetic issue, they are now made via nanotechnology to form a more transparent film on the skin of either titanium dioxide or zinc oxide. Recently there have been concerns on skin penetration and absorption of these nanoparticles. Some studies have been done on sunscreen absorption which show titanium dioxide and zinc oxide do not penetrate beneath the stratum corneum layer of the skin and are not likely to cause harm (7). Titanium dioxide has been classified as a carcinogen by the European Union, however, this is more regarding the inhaled form and it is unclear whether it is relevant to skin application (8).
Of note, the American Academy of Dermatology recommends using mineral sunscreens in babies, such as zinc oxide because it is less likely to irritate a baby’s sensitive skin (9). From What To Expect, a popular parenting website, Yale Dermatologist Dr. Deanne Mraz Robinson MD states, “A sunscreen with zinc is your best bet — it's the same ingredient in most diaper rash creams…It creates a barrier to protect the skin and is highly tolerable for even the most sensitive skin (10).”
Personally, having read the most up to date information for physicians, I would choose a Zinc Oxide based sunscreen for myself and my family due to the highest safety profile so far among all the options. It is also paramount to make sure the remainder of the ingredients in the sunscreen are natural. Avoid any preservatives such as methylparabens (increasing concerns about cancer) or phenoxyethanol (immune or allergenic effects).
When purchasing a safe sunscreen, look for something that has zinc oxide as its only active ingredient, and is chemical- and preservative- free.
1. Matta MK, Zusterzeel R, Pilli NR, et al. Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial. JAMA 2019; 321:2082.
3. Scinicariello F, Buser MC. Serum Testosterone Concentrations and Urinary Bisphenol A, Benzophenone-3, Triclosan, and Paraben Levels in Male and Female Children and Adolescents: NHANES 2011-2012. Environ Health Perspect. 2016;124(12):1898-1904.
7. Pflücker F, Wendel V, Hohenberg H, et al. The human stratum corneum layer: an effective barrier against dermal uptake of different forms of topically applied micronised titanium dioxide. Skin Pharmacol Appl Skin Physiol 2001; 14 Suppl 1:92.