FREQUENT QUESTIONS ABOUT HOCl
General
Hypochlorous acid is a free chlorine molecule with the chemical structure HOCl. It is the dominate free chlorine species in chlorine solutions that have a slightly acidic to neutral pH. HOCl is a much more powerful oxidant than sodium hypochlorite (or chlorine bleach).
Hypochlorous acid is produced naturally by the white blood cells of all mammals. It is used by white blood cells to kill invading microbial pathogens.
Hypochlorous acid (HOCl) is a neutrally charged molecule. Bacteria have negatively charged cell walls. Just like magnets, molecules with the same charge will repel each other. For example, the negatively charged molecule of bleach (OCl-) is repelled by bacterial cell walls. This is not the case with HOCl which is neutrally charged. HOCl easily penetrates bacterial cell walls. HOCl either oxidizes the cell walls killing the bacteria or enters through the cell walls and destroys the vital components inside the bacteria.
Unlike many other sanitation chemicals, hypochlorous acid does not have an ongoing antimicrobial effect. In other words, once it lands on a surface, it reacts with any germs or organic matter on that surface and then immediately deactivates. This is good and bad. It is good because it allows for sanitation without requiring a post-rinse because no toxic chemicals are left behind. The disadvantage is that it has to be continuously applied.
Production & Stability
Hypochlorous acid is made through a process called electrolysis. By passing a sodium chloride solution (NaCl) through an electrolysis cell containing an anode and a cathode, electrolyzed water is generated. There are two commonly used electrolysis methods for generating hypochlorous acid, membrane cell electrolysis and single cell electrolysis. Membrane cell electrolysis converts a saltwater brine into two solutions, a strongly acidic anolyte of hypochlorous acid and a strongly alkaline catholyte of sodium hydroxide. Single cell electrolysis converts a saltwater brine into one solution, a slightly acidic-to-neutral anolyte of hypochlorous acid.
Hypochlorous acid can be made from chlorine bleach by dilution however there are limitations. Hypochlorous acid is almost nonexistent in a free chlorine solution with a pH above 9. Chlorine bleach has a pH above 13. By diluting chlorine bleach, the pH can be lowered however the concentration of free chlorine will also be lowered. Upon diluting chlorine bleach to pH 8.5, the percent of the free chlorine that is hypochlorous acid is less than 5%. More dilution will dilute the free available chlorine concentration to unuseful levels. Trying to lower the pH with acidifiers will not help either because chlorine bleach will react violently and the free available chlorine product will be lost as chlorine gas. Therefore, electrolysis is the only safe method for generating high concentrations of acidic-to-neutral pH free chlorine solutions that are dominated by hypochlorous acid. At pH 5, the percent of free chlorine that is hypochlorous acid is above 99%.
Depending on the process used to generate the hypochlorous acid, the solution can be stable. Membrane cell electrolysis generates two streams with opposing oxidation-reduction potentials and opposite pH. This is done by forcing positively charged sodium ions across a membrane toward the cathode side. On the anode side, a very high concentration of anolyte is generated that is strongly acidic (~ pH 3). Generating hypochlorous acid by this method is not as stable as that generated by single cell technology. Single cell technology uses an acidified brine and only one stream of solution is generated in the pH range of 5-7. When generating hypochlorous acid through a single cell, no high pressures are used and no ions are forced across a membrane. The hypochlorous acid generated is stable, not seeking a new equilibrium like the anolyte generated from membrane cell systems.
The shelf-life can be 3-6 months if stored in a closed container protected from the oxygen in the air. Containers that block out UV light may have a small effect on extending shelf-life.
Hypochlorous acid is a strong oxidant that is seeking to steal electrons from another molecule. Synthetic surfaces are difficult to steal electrons from however organic matter, microbial pathogens, or oxygen in the air is easy to steal electrons from. Once hypochlorous acid steals an electron, it either binds to that molecule and forms a new molecule, reverts back to hypochlorite, or it turns back into saline.
Effectiveness & Proof
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 indicated that HOCl is more effective than OCl- (aka. chlorine bleach) 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- (click here to visit research database). HOCl may be more effective than OCl- for two reasons, this first is because it holds a neutral charge and therefore can easily penetrate the negatively charged cell walls of bacteria. The second reason is because HOCl has a much higher oxidation potential than OCl-.
Hypochlorous acid (HOCl) has been researched and proven to be effective against many viruses Click here to visit research on viruses.
Yes, hypochlorous acid is very effective at removing biofilm and preventing formation. Click here to visit research on biofilm.
The concentration that should be used depends on the application. Sanitizing food such as fruits & vegetables and fish & seafood is highly effective at 20-30 ppm however the FDA allows concentrations to be used as high as 60 ppm without requiring a post rinse. Sanitizing food contact surfaces is also effective at 20-30 ppm however concentrations as high as 200 ppm are allowed by the FDA. Water disinfection is effective at 1-2 ppm however the EPA allows up to 4 ppm. When deciding what concentration to use, it is best to refer to the research. Over 300 research articles have been published covering nearly every application. Click here to visit the research database organized by industry.
Hypochlorous acid is measured with the same standard test strips that measure free chlorine in a pool. The test strips will turn a different shade of purple to indicate the concentration between 10 and 200 ppm. For higher concentrations, the solution being tested can be diluted. (Example: A 1000 ppm solution could be diluted at a 1:10 ratio. A test strip would then read 100 ppm indicating the original solution was 1000 ppm.)
Over 300 research articles have been published covering nearly every application. Click here to visit the research database organized by industry.
The most researched applications have been in the food industry using hypochlorous acid for direct food sanitation and for sanitation of food contact surfaces. Other researched applications have been in healthcare for disinfection and sterilization of equipment, for wound care, and for general sanitation of healthcare facilities against MRSA and spore forming organisms. Additionally, research has been done in the industry of livestock, agriculture, and for water treatment and disinfection. Click here to visit the research database organized by industry.
Yes, probably the most research on hypochlorous acid has been done on the microbial pathogens Listeria, Salmonella, and E. coli. Click here to visit the research database organized by microbial pathogen.
Hypochlorous acid is highly effective against MRSA. Click here to see the research on MRSA. Since Clostridium specias are difficult to culture in the lab, Bacillus species, which are also spore forming bacteria and more difficult to kill, are used instead. Click here to see the research on Bacillus .
Yes, there are two published studies on Norovirus. Click here to see the research on Norovirus.
Safety & Environment
Hypochlorous acid is non-toxic and non-hazardous. Unlike most chemical sanitizers, hypochlorous acid is non-irritant to eyes, skin, and the respiratory tract. Even if it were ingested by accident, it causes no harm.
Yes, the majority of the research on hypochlorous acid has been for using hypochlorous acid directly on food. The FDA Food Contact Notification 1811 allows for hypochlorous acid to be used on raw or processed fruits & vegetables, fish & seafood, meat, poultry and shell eggs at up to 60 ppm. Click here to see FCN 1811 at the FDA website.
Hypochlorous acid does not change the taste or smell of food when used at FDA cleared concentrations.
The FDA clearance of a food contact substance requires that it not leave behind any harmful residues. Hypochlorous is cleared for use at up to 60 ppm.
Yes, hypochlorous acid is 100% safe and non-irritant. It is safe enough to be used on personal items such as toothbrushes, baby pacifiers, and toys for pets.
Hypochlorous acid is much less aggressive on fabrics than peroxide or chlorine bleach. Although hypochlorous acid usually does not cause bleaching or discoloration, some lower quality dyes may bleed when exposed to hypochlorous acid.
Hypochlorous acid is a powerful oxidant and will cause corrosion if left exposed for extended periods of time to brass, copper, iron, or lower quality steel. Stainless steel can corrode as well if submersed in high concentrations of hypochlorous acid (>200 ppm) for extended periods of time.
Industry & Application
Hypochlorous acids (HOCl) is being used in restaurants, food & beverage processing, livestock, agriculture, hospitals, schools, cruise ships, water treatment, and pharmaceutical manufacturing.
Hypochlorous acid (HOCl) is used by restaurants as a no-rinse sanitizer for produce, meat, poultry, and seafood. HOCl prolongs shelf-life. HOCl is used for sanitation of food contact surfaces as well as for sanitation of all kitchenware, cutting boards, cutlery, and utensils. HOCl makes a great hand sanitizer. It also replaces toxic chemicals used for cleaning sinks, bathrooms, and floors. HOCl is used to clean tables and seating areas of the restaurant. It can be applied via hoses or foggers to broadly disinfect large areas.
Hypochlorous acid (HOCl) replaces water in produce washers for cleaning and sanitizing fruits and vegetables as a no-rinse sanitizer and prolongs the shelf-life. HOCl is used to sanitize equipment and work areas. HOCl can be applied via hoses or foggers to broadly sanitize large areas. Employees can step into foot bathes and be misted by HOCl when entering a processing facility.
Hypochlorous acid (HOCl) is safe on animals and has many applications in the poultry industry including hatcheries, broiler houses and processing. HOCl can be applied to eggs in hatcheries via misting and is cleared by FDA FCN 1811. Hypochlorous acid can be dosed into the drinking water for broiler houses at up to 4 ppm to ensure sterile water. It can be applied via sprinklers and misters to maintain a sanitized environment for chickens, increasing growth rates and decreasing feed to growth ratios. HOCl can be used to sanitize whole or processed chickens as a no-rinse sanitizer at processing using concentrations up to 60 ppm per FDA FCN 1811. HOCl can be applied via hoses or foggers to broadly sanitize large areas. Employees can step into foot bathes and be misted by HOCl when entering a processing facility.
Hypochlorous acid (HOCl) is safe on animals and has many applications for livestock and meat processing. Hypochlorous acid can be applied to living areas to maintain clean and sanitized environments. HOCl can be dosed into the water for sterile drinking water. HOCl is used for sanitizing raw carcusses as a no-rinse sanitizer for processing. HOCl can be applied via hoses or foggers to broadly sanitize large areas. Employees can step into foot bathes and be misted by HOCl when entering a processing facility.
Hypochlorous acid (HOCl) can be used at harvest and processing to sanitize raw seafood as a no-rinse sanitizer at up to 60 ppm per FDA FCN 1811. HOCl can be dosed in the water for creating sanitized ice for storing or displaying seafood. It can be applied via hoses to clean equipment and sanitize work areas. Employees can step into foot bathes and be misted by HOCl when entering a processing facility.
Hypochlorous acid (HOCl) can generate sterile water for dairy and beverage manufacturing. HOCl is used to disinfect bottles. HOCl can dislodge biofilm and disinfect pipes in clean-in-place systems. It can be applied via hoses to clean equipment and sanitize work areas. Employees can step into foot bathes and be misted by HOCl when entering a processing facility.
Hypochlorous acid (HOCl) can be used to sanitize linens. HOCl can be used to disinfect contact surfaces and can be applied broadly to rooms and common areas via foggers. HOCl replaces concentrated toxic chemicals for cleaning and disinfecting sinks, bathrooms, and floors. HOCl can be used as hand sanitizer for staff and guests via dispensers.
Hypochlorous acid has many useful applications on a cruise ship. HOCl can be used in the kitchen as a no-rinse sanitizer for produce, meat, poultry, and seafood. HOCl can be used as a sanitizer on food contact surfaces and for general sanitation replacing quats and peroxide based chemicals. It can be applied via foggers or misters to broadly disinfect rooms and large common areas. HOCl can be used to clean and disinfect the ship for prevention and control of Norovirus outbreaks. HOCl can be used as hand sanitizers via dispensers throughout the ship. HOCl can replace chlorine for generating potable water and for pool treatment.
Hypochlorous acid (HOCl) replaces chlorine in pool treatment. HOCl is non-irritant and is safe on eyes and skin.
Hypochlorous acid (HOCl) can be used to sanitize linens. HOCl can replace toxic concentrated chemicals for cleaning and disinfecting rooms and common areas. HOCl can be applied via foggers to broadly disinfect rooms and the air. HOCl can be used in the hospital kitchen as a no-rinse sanitizer for produce, meat, poultry, and seafood. It can be used to clean and disinfect all contact surfaces and kitchenware. HOCl can be placed throughout hospitals in dispensers for hand sanitation.
Hypochlorous acid (HOCl) can be used to maintain sterile environments for pharmaceutical manufacturing. HOCl dislodges biofilm and disinfects pipes for clean-in-place (CIP) systems. HOCl can be used for cold sterilization of equipment and instruments.
Hypochlorous acid (HOCl) can replace toxic concentrated chemicals for cleaning and disinfecting school rooms and common areas. HOCl can be applied via foggers to broadly disinfect rooms and the air. HOCl can be used in the school kitchen as a no-rinse sanitizer for produce, meat, poultry, and seafood. It can be used to clean and disinfect all contact surfaces and kitcheware. HOCl can be placed throughout schools in dispensers for hand sanitation.
Hypochlorous acid is safe on animals and can replace chemicals used to sanitize living environments in the zoo.
Hypochlorous acid is ideal for CIP systems. Hypochlorous acid dislodges biofilm and disinfects pipes.
Regulation
The FDA cleared hypochlorous acid per FCN 1811 to be used for the following applications at up to 60 ppm: Hypochlorous acid may may be used in processing facilities at up to 60 ppm for use in process water or ice which comes into contact with food as a spray, wash, rinse, dip, chiller water, and scalding water for whole or cut meat and poultry, including carcasses, parts, trim, and organs; in process water, ice, or brine used for washing, rinsing, or cooling of processed and pre-formed meat and poultry products as defined in 21 CFR 170.3(n)(29) and 21 CFR 170.3(n)(34), respectively; in process water or ice for washing, rinsing or cooling fruits, vegetables, whole or cut fish and seafood; and in process water for washing or rinsing shell eggs. Click here to see FCN 1811 at the FDA website.
The maximum concentration that can be used directly on food as a no-rinse sanitizer is 60 ppm per FDA FCN 1811. Click here to see FCN 1811 at the FDA website.
The maximum concentration that can be used on food contact surfaces is 200 ppm per the EPA. Click here to see EPA Code of Federal Regulations.
Hypochlorous acid does not require a post-rinse when sanitizing food at or below 60 ppm. Click here to see FCN 1811 at the FDA website.
On June 9, 2014, the National Organic Program (NOP) published a policy memorandum clarifying that electrolyzed water (hypochlorous acid) is allowed in organic production and handling. Click here to see USDA Organic memorandum.
The EPA allows for hypochlorous acid to be used for disinfecting drinking water at a concentration up to 4 mg/L (or 4 ppm). Click here to see National Primary Drinking Water Regulations.