What Is Hypochlorous Acid?

CDC's disinfection guideline says the microbicidal activity of chlorine is attributed largely to undissociated hypochlorous acid, or HOCl, which converts to the less microbicidal hypochlorite ion as pH rises, so chlorine's disinfecting efficacy decreases at higher pH. A 2020 review in Cellular and Molecular Life Sciences says HOCl is most commonly implicated as the reactive species responsible for killing microbes inside white blood cells called neutrophils, and describes it as a strong oxidant that is also the active ingredient of household bleach.

Some products make it on demand. CDC describes superoxidized water made by electrolyzing saline, whose main products are hypochlorous acid, at about 144 mg/L, and chlorine. In a May 22, 2025 letter, the EPA found an amended label for a registered disinfectant system acceptable under the federal pesticide law, and the company's label says its appliance uses electricity, tap water and an activator capsule to create a hypochlorous acid solution of 220 ppm available chlorine by electrolysis.

Skin and eye products fall under the FDA. In an April 21, 2025 letter, the FDA found a hypochlorous acid skin and wound cleanser substantially equivalent to legally marketed predicate devices under the 510(k) process, and the company's summary describes it as about 99.94 percent water and 0.036 percent hypochlorous acid, which it says functions as a preservative. In a November 2, 2020 warning letter, the FDA said a company's 0.01 percent hypochlorous acid lid and lash solution was offered as intended to mitigate, prevent, treat, diagnose or cure COVID-19, making it an unapproved new drug.