Hypochlorous and hypochlorite (bleach) both come from the same family of chlorine-based disinfectants and share similar chemical structures. So what makes hypochlorous a better choice?

There are many reasons why hypochlorous is a far superior disinfectant than bleach, but one of the most fundamental reasons has to do with pH. Hypochlorous acid exists at a near-neutral pH (5-7). Bleach resides at a highly-alkaline pH (8-13). The germ-killing properties of bleach are derived from the presence of hypochlorous acid. However, because of its high pH, the majority of the hypochlorous acid present in bleach ends up getting converted to hypochlorite, which is a less effective disinfectant.

The pH of a chlorine solution is crucial in determining its efficacy. At pH 5-6, the solution will be nearly 100% hypochlorous acid. As the pH increases above 6, hypochlorite (bleach) begins to increase.

This graph shows that when the pH is between 4-7, hypochlorous (HOCl) dominates the solution. When the pH rises above 7, hypochlorite (OCl-) dominates.

White's Handbook of Chlorination states, "[Hypochlorous] is overall the most effective disinfectant of the chlorine species present in dilute solution at the pH values associated with water and wastewater treatment. The OCl- ion [bleach] is a relatively poor disinfectant because of its inability to diffuse through the cell walls of microorganisms."

Why can't bleach diffuse through pathogen cell walls? Both pathogens and bleach carry a negative charge, which means that when bleach encounters a pathogen, it repels the pathogen like two magnets. Because hypochlorous is neutrally-charged, it can break past the pathogen cell wall and inactivate it from the inside out. This process is the same way our immune system fights off pathogens. In fact, our white blood cells produce hypochlorous acid during the immune response!

Switching from using bleach to hypochlorous as a sanitizer is not complicated at all, but it may mean you need to adjust some of your cleaning protocols. For example, cleaning the area with regular soap and water first to remove the bulk of organic material present allows your sanitizer (hypochlorous acid) to disinfect much more effectively. Otherwise, the chlorine in the hypochlorous gets used up trying to break down the organic matter, instead of focusing on killing the more resilient pathogens.

Hypochlorous acid is much stronger as a disinfectant than bleach, but it actually has lower pH, salt content, and parts per million of chlorine. You can use less hypochlorous acid and still get the same (or better) effect as you would with bleach. Think of it like the difference between two currencies. If the euro is stronger than the dollar, then an item will cost less in euros than it will in dollars.

In the table below, you can see comparisons between the kill claims for hypochlorous acid and bleach. In full disclosure, the information presented here is based on a review of the available peer-reviewed literature for kill claims on both hypochlorous acid and sodium hypochlorite. The studies were done independent of each other and thus the selected ppm and pH of each chemical tested was left to the deliberation of the researchers.

Studies that compare the two disinfectants head to head are rare, so this graph is not meant to be used as an exact guide for replacing hypochlorous with bleach. It's purpose is to give the reader a general idea of the differences in chlorine content and disinfecting power between the two solutions. The current body of research suggests that 200 ppm hypochlorous is potent enough to inactivate the majority of enveloped viruses within a range of 0.5 - 5 minutes.

And if you're looking for specific ratios for switching between hypochlorous and bleach, check out this article!

Cover Photo by Clay Banks on Unsplash  

References

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