Hypochlorous Acid

Hypochlorous Acid (HClO or HOCl), is a naturally occurring substance in our bodies and the same chemical that our own white blood cells produce to fight infection and kill pathogens through oxidation and chlorination. As a disinfectant, Hypochlorous Acid solution, while being non-toxic to the cells in our body, is lethal to all known dangerous bacteria and viruses that threaten our health.

Being first used over 175 years ago, Hypochlorous Acid sometimes known as anolyte water is a liquid produced through a process called electrolysis, a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Specifically, engineered electrolysis cells can generate a solution of free chlorine species by running electricity through NaCl (table salt) and water.


IUPAC Name : Hypochlorous acid, chloric(I) acid, chloranol, hydroxidochlorine

Other Names : Hydrogen hypochlorite, chlorine hydroxide, electrolyzed water, electrolyzed oxidizing water, electro-activated water

CAS Number : 7790-92-3

Molar Mass : 52.46 g/mol

Molecular Formula : HOCl

Appearance : Colorless aqueous solution

Solubility in water : Soluble

Acidity : 7.53

Hypochlorous acid is a weak acid (pKa of about 7.5), meaning it dissociates slightly into hydrogen and hypochlorite ions as noted in equation : HOCl ⇌ H+ + OCl-

Between a pH of 6.5 and 8.5 this dissociation is incomplete and both HOCl and OCl- species are present to some extent. Below a pH of 5, no dissociation of HOCl occurs, while above a pH of 11, complete dissociation to OCl- occurs.

The germicidal efficiency of hypochlorous acid (HOCl) is much higher than that of the hypochlorite ion (OCl-). The distribution of chlorine species between HOCl and OCl- is determined by pH, as discussed above.

Bacteria Inactivation

Chlorine is an extremely effective disinfectant for inactivating bacteria. A study conducted during the 1940s investigated the inactivation levels as a function of time for E. coli, Pseudomonas aeruginosa, Salmonella typhi, and Shigella dysenteriae (Butterfield et al., 1943 ). Study results indicat ed that HOCl is more effective than OCl- for inactivation of these bacteria. These results have been confirmed by several researchers that concluded that HOCl is 70 to 80 times more effective than OCl- for inactivating bacteria (Culp/Wesner/Culp, 1986 ). Since 1986, there have been hundreds of publications confirming the superiority of HOCl over OCl- (see the research ).

This biggest challenge has been to create hypochlorous acid at a near neutral pH instead of chlorine gas or hypochlorite, and to do so in a stable form. Hypochlorous acid is a meta-stable molecule. It wants to revert back to salt water or convert to hypochlorite.


Hypochlorous acid is one of the most effective known biocides. The chemical structure is HOCl. It is produced by the human immune system to kill invasive organisms and fight infection. White blood cells in the human immune system produce hypochlorous acid through the myeloperoxidase-mediated peroxidation of chloride ions.White blood cells release this natural oxidant to fight invading pathogens.

When a wound breaks human skin, it creates a gateway for harmful pathogens to invade human cells.Neutrophils, which are a type of white blood cell, travel in the blood to the site of the wound where the pathogens are invading. When an invading pathogen or infection threatens a human cell, the body's immune system responds by destroying the pathogen before it can harm the cell.The invading pathogens are engulfed by white blood cells through a process called phagocytosis. Once engulfed, the white blood cell produces an oxidant, hypochlorous acid.Hypochlorous Acid is a biocide and kills the microbial pathogen within milliseconds of contact.This antimicrobial process is called the Oxidative Burst Pathway.

Technology & Research

The use of chlorine for disinfection has been researched for over 100 years. It has been an undisputable fact that hypochlorous acid offers far superior disinfecting properties than sodium hypochlorite (chlorine bleach). One of the most well known authorities for the use of chlorine as a disinfectant is White's Handbook of Chlorination. This book is comprehensive in explaining the chemistry and effectiveness of chlorine and alternative disinfectants.

The challenge has been in engineering a system for producing a free chlorine solution that is dominated by the molecule of hyopchlorous acid (HOCl) rather than sodium hypochlorite (NaOCl). The development of electrolysis cells for generating electrolyzed water became a huge innovative breakthrough in the 1970s. Since then, improvements in electrolysis cells have been made that can generate a solution of free chlorine that is near 99% hypochlorous acid and that is stable.

One of the most recent improvements has been the development of single cell technology to replace membrane cell technology allowing for the production of just one stream of solution at a near neutral pH. Prior technology used membranes and high pressures that forced two streams to be generated, an unstable anolyte of hypochlorous acid and an unstable catholyte of sodium hydroxide. With the development of single cell technology, a stable solution of just anolyte can be produced yielding a solution of near 99% stable hypochlorous acid.

Over 30 years of research exisits for the use of hypochlorous acid and new research is being published every year. Recent research has focused on the use of hypochlorous acid for sanitzing food and food processing facilities. Research has also been done on poultry farms, water treatment and disinfection, and healthcare related applications such as wound care and equipment sterilization.