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The Truth About Hypochlorous Acid (HOCl)

With a long scientific history and many promising attributes, it is hard to understand why hypochlorous acid (HOCl) – based disinfectants aren’t used in every commercial cleaning operation.1-3 In one recent review article focusing on the use as a disinfectant, the authors concluded that HOCl “comprises many of the desired effects of the ideal disinfectant: It is easy to use, is inexpensive, has a good safety profile, and can be used to disinfect large areas quickly and with a broad range of bactericidal and virucidal effects.”4,5 The reason is, as with most things, the devil is in the details. In this blog, I’ll break down those details by answering these questions:

  • What is HOCl?
  • How are HOCl-based solutions made and sold?
  • Which HOCl-based solution is right for you?

What is HOCl?

HOCl is a weak acid that is formed when chlorine (a gas) dissolves in water. It is used as an active ingredient in sanitizers and disinfectants because of its ability to break apart cell membranes, similar to the mechanism of action of sodium hypochlorite (bleach) or hydrogen peroxide. Water solutions of HOCl are in the neutral to slightly acidic pH range. HOCl has many other common names (not all technically accurate) including  “electrolyzed water,” “activated water,” “enhanced water,” “superoxidized water,” and the most technically inaccurate of all is “no-chemical” (because everything, even water, is a chemical!).

HOCl is surprisingly effective at very low concentrations. It takes only a very small amount of HOCl to effectively kill bacteria and viruses and destroy proteins like inanimate pet allergens in comparison to higher pH bleach-based products. Despite this outstanding ability, it is also gentle on surfaces, and when no additional ingredients like surfactants or detergents are added to the final formula, HOCl solutions leave behind minimal residue. Evidence of this is demonstrated by the HOCl-based solutions on the market that are EPA approved as food contact sanitizers. These products do not require a rinse step when used on surfaces that come into contact with food.

How are HOCl-based solutions made and sold?

There are three main ways that HOCl-based solutions are made and sold:

  1. Ready to Use (RTU) products are typically made by adjusting the pH of a sodium hypochlorite (bleach) solution at the manufacturing plant. To do this, a solution of sodium hypochlorite, which is typically basic (or alkaline) on the pH scale, is brought down to a neutral pH by adding a pH-adjustor.
  2.  In onsite generation systems, electricity is run through a brine of salt and water. To do this, salt (or sometimes called a “precursor”) is added to water prior to the electricity being applied.
  3.  There are also tablet products that are capable of making HOCl solutions on site as well. Sodium dichloroisocyanurate (NaDCC or SDIC) is a colorless, water-soluble solid that creates HOCl when it dissolves in water.

Which HOCl-based solution is right for you?

As with all products, there are pros and cons, and this holds true for HOCl-based solutions too. All HOCl-based solutions offer some promising benefits in regards to safety and surface compatibility, but there are also some watch outs to be aware of. Below is a table that highlights the differences between the three common types of HOCl-based solutions and a list of questions that can be used to assess any HOCl-based product before you buy.

Table: Pros and Cons of three common types of HOCl-based solutions

ProsCons
Ready to Use (RTU)• Safety profile
• Longer shelf life (generally 1 year)
• Guaranteed concentration and micro-efficacy and
• No upfront device costs
• No contamination risk
• No bottles to clean
Higher price per bottle Bottles may not be reusable
On-site generated• Safety profile
• Only make what you use
• Cost less per oz. (after system purchase)
• Shorter shelf life (days to weeks)
• Up front cost of system
• Cost of system maintenance
• More work/more steps for end users
• Bottles must be cleaned between uses
• Concentration and efficacy not guaranteed
Tablet• Safety profile (of final solution)
• Lower shipping costs (no liquid)
• Takes up less room in storage
• Long shelf life (of tablet)
• No upfront device cost
• Longer contact times
• Shorter shelf life when in solution (days to weeks)
• Toxicity of concentrated tablet form (wear gloves and goggles when dissolving)
• Dissolving can take time
• Bottles/dissolving containers must be cleaned between uses
• More work/more steps for end users
 

Questions to ask about all HOCl-based solutions before you buy:

  • Is it EPA-registered? RTU and tablets should have an EPA registration number on the product label. Onsite generation systems may not have an EPA registration because the HOCl-based solution is not made until after the product is sold. Also, watch out that you are not confusing EPA establishment numbers for EPA registration numbers. These are two different things!6
  • Does it disinfect and/or sanitize? Disinfectants are EPA registered to kill illness-causing bacteria, viruses, and sometimes fungi, while sanitizers are only EPA registered to kill illness-causing bacteria.
  • What is the contact time? As with any product, shorter is usually better, but longer contact times can be acceptable in some cases. Contact times should always be built into your processes so that cleaners don’t have downtime while the product works. In some cases, if HOCl solutions do not need to be rinsed, then longer contact times may be acceptable because they won’t impact the speed of your cleaning processes.
  • Does it contain a surfactant (aka detergent)? Many HOCl products on the market do not contain a surfactant, but some do. Products that do not contain surfactants can be great for routine, preventative cleaning and disinfecting, but a second product that contains a surfactant may be needed to handle tougher cleaning jobs prior to disinfecting. Solutions that contain surfactants are more likely to leave behind a residue that will need to be wiped off.
  • Is it safe to use through an electrostatic sprayer? Not all HOCl-based solutions have been EPA approved to be used through electrostatic sprayers, which means they haven’t been confirmed for safety and microbial efficacy. Check the products master label before utilizing electrostatic applicator technology with HOCl-based solutions.
  • Is it considered food-contact safe? HOCl-solutions that are food-contact safe do not need to be rinsed or wiped after use. This can save you time and give your building occupants and management peace of mind. Again, check the EPA master label to confirm the directions for use.

Using the pros and cons list and answering the above questions can help you narrow in on which option to purchase but remember this important implementation tip: Start small with implementing any new product (test it with one crew, in one area for a predetermined amount of time) and don’t make further changes until you have reason to believe that the product is a benefit to your organization. Changes, even great ones, take time.

CloroxPro and Clorox Healthcare are proud tooffer two RTU HOCl-based solutions for consideration in your organization. You can learn more about them here:

References:

1. Smith JL, Drennan AM, Rettie T, Campbell W. Experimental Observations on the antiseptic action of hypochlorous acid and its application to wound treatment. Br Med J. [Internet] 1915 Jul 24; 2(2847):129-36. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2302602/pdf/brmedj07241-0005.pdf
2. Garibyan, Lilit et al. Advanced aging skin and itch: addressing an unmet need. Dermatologic therapy [Internet] 2013 26(2): 92-103. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4051285/
3. Moorman E, Montazeri N, Jaykus L-A. Efficacy of neutral electrolyzed water for inactivation of human norovirus. Appl Environ Microbiol [Internet] 2017 Aug 1; 83(16). Available from:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5541222/
4. Block MS, Rowan BG. Hypochlorous acid: a review. J Oral Maxillofac Surg [Internet] 2020 Sep; 78(9): 1461–1466. Available from:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7315945/
5. CDC. Guideline for Disinfection and Sterilization in Healthcare Facilities (2008) Properties of an ideal disinfectant. [Internet] 2008. Available from: https://www.cdc.gov/infectioncontrol/guidelines/disinfection/tables/table2.html
6. EPA Label Review Manual Chapter 14: Identification Numbers. [Internet] 2012. Available from: https://www.epa.gov/sites/production/files/2015-03/documents/chap-14-nov-2012.pdf