As if having acne wasn’t stressful enough, there is now compelling scientific data that shows benzyl peroxide, a popular acne treatment, could also be making us age faster. Let’s understand how this product is made to learn more of how it works on the skin.

Chemistry 101

Benzyl peroxide is usually prepared by treating hydrogen peroxide with benzoyl chloride. The oxygen-oxygen bond in peroxides is weak, so, benzyl peroxide readily undergoes homolysis (symmetrical fission), forming free radicals:

[C6H5C(O)]2O2 → 2 C6H5CO2•

The symbol • indicates that the products are radicals; i.e., they contain at least one unpaired electron known as a free radical. This is an electron that doesn’t have a buddy and so it’ll latch onto anything that lets it have a friend. Electrons like to be in even numbers: 0, 2, or 8. If there’s an odd number of electrons (like 5), then obviously you have some number of paired electrons (in the case of 5, you have two pairs), and one left over. It’s that one left over that will now try and steal an electron from a neighboring molecule to stabilize itself. Such species are highly reactive.

Once this free radical forms and it succeeds in gaining another electron from a nearby molecule, it leaves its victim short an electron and has now made this new molecule, a free radical, which in turn, will try and steal an electron as well. And so begins an enormous chain reaction of free radicals that quickly wreaks havoc on living tissue. It is estimated that a chain reaction can trigger 6.023 x 1021 billion molecules to react per second.

How benzyl peroxide works on acne

Acne blemishes are usually filled with oil, bacteria and dead skin cells. Treatments to help this skin condition are designed to breakdown the debris and clean it out. It’s the hydroxyl radicals that are often referred to as the “detergent” in these formulas because they often react with pollutants forming the first step in their removal. Additionally, these free radicals have strong bactericidal activity that works to kill any present bacteria. You will sometimes see an antioxidant like green tea in a product containing benzyl peroxide, manufacturers put it in there as an antioxidant to help counteract the free radical activity. However, we have to ask ourselves, it is enough antioxidant activity to quench the damaging effects over time?

Scientific concerns and observations

UCLA researchers recently found that combining resveratrol with benzyl peroxide may enhance the drug’s ability to kill the bacteria and could translate into new treatments. Resveratrol stops the formation of free radicals, which cause cell and tissue damage. benzyl peroxide, on the other hand, is an oxidant that works by creating free radicals that kill acne bacteria. Emma Taylor, assistant clinical professor of medicine in the Division of Dermatology states; “we initially thought that since the actions of the two compounds are opposing, their actions should cancel each other out, but it didn’t”. After further testing, they found that benzyl peroxide was able to initially kill the acne causing bacteria at all concentration levels, but the effect was short-lived and didn’t last beyond the first 24 hours. Resveratrol didn’t have a strong killing capability, but it inhibited bacterial growth for a longer period of time. ¹

The Department of Environmental Health Sciences, Johns Hopkins Medical Institutions found that although not mutagenic, benzyl peroxide has been observed to produce strand breaks in DNA of exposed cells. These actions are presumed to be mediated by free-radical derivatives of benzyl peroxide. ²

Studies have highlighted the carcinogenic potential of benzyl peroxide. A 1981 study from the Journal of Science concluded, “caution should be recommended in the use of this and other free radical-generating compounds” ³

Harvard Medical School, Boston MA and Wellman Laboratories of Photo-medicine, Department of Dermatology, Massachusetts General Hospital, published results of their study in the Journal of Investigative Dermatology that showed repeated chronic treatment with benzyl peroxide caused changes which resemble those caused by low fluence UVB and are quite distinct from other chronic inflammatory skin disorders. This suggests that common inflammatory mechanisms may be involved in the production of the changes seen with chronic UVB or benzyl peroxide exposure. It is likely that free radical generation, alteration of anti-oxidant capacity or a combination of both is implicated and the findings provide further support for the role of oxidative stress in the photo aging process. ⁴

Even the Food and Drug Administration (FDA) on their own website are warning that the use of certain acne products containing the active ingredients benzyl peroxide or salicylic acid can cause rare but serious and potentially life-threatening allergic reactions or severe irritation. An active ingredient is the component that makes the medicine effective against the illness or condition it is treating. Products of concern are marketed under different brand names such as Proactiv, Neutrogena, MaxClarity, Oxy, Ambi, Aveeno, and Clean & Clear.⁵

  • (1) “Resveratrol Demonstrates Antimicrobial Effects against Propionibacterium acnes in Vitro,” Dermatology and Therapy, September 2014.
  • (2) Role of the benzoyloxyl radical in DNA damage mediated by benzoyl peroxide.Swauger JE, Dolan PM, Zweier JL, Kuppusamy P, Kensler TW. Department of Environmental Health Sciences, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
  • (3) “Skin tumor-promoting activity of benzoyl peroxide, a… [Science. 1981] – PubMed – NCBI”. 2012-05-24. Retrieved 2012-09-08
  • (4) Journal of Investigative Dermatology (1999) 112, 933–938; doi:10.1046/j.1523-1747.1999.00591.x For more clinical date on the effects of Benzyl Peroxide visit
  • (5) Topical Acne Products Can Cause Dangerous Side Effects