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What Is Hypochlorous Acid?

Mary McMahon
Updated May 21, 2024
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Hypochlorous acid is a weak acid that can only exist in solution, because it is highly unstable when isolated in a pure form. There are a number of uses for this chemical, most of which take advantage of its strong oxidizing properties, which allow it to be used in bleach and disinfectant, among many other things. Many manufacturers produce this acid for sale to both industrial users and ordinary consumers, and many stores carry it, typically in the household cleaning section. Though it can be safely used when diluted, it can be very dangerous when concentrated.

The chemical formula for this compound is HClO. It is classically obtained by dissolving chlorine in water, although it can also be obtained by reacting chlorine with mercury(II) oxide to create a pure form, which is greenish-yellow in color. The "chlorine bleach" sold for disinfectant and laundering contains hypochlorous acid, and the systems used to chlorinate many water supplies rely on it to kill unwanted microorganisms in the water, with the acid creating conditions that make life unsustainable for these microbial invaders.

While this compound can be very useful in many applications, including household laundry, cleaning, and sterilization of clinical environments, it can also be dangerous in certain settings. It can also cause skin irritation and damage to the eyes, and people should use caution or wear protection when working with it to avoid splashbacks.

In bleaching, the acid acts to oxidize the agents that cause stains. This strong oxidizing power can also make the chemical very dangerous, because it can become explosive in certain settings. Adding acids to a solution that contains it will precipitate this process, making the mixture unstable, releasing chlorine gas, and potentially causing an explosive chemical reaction.

In disinfecting, a solution with a pH balance of around five to six is usually optimal. The compound needs to be handled carefully because it can release dangerous chlorine gas if it is mixed with the wrong chemicals. Chlorine gas can cause considerable health problems or death, especially in a space that is poorly ventilated, which is one reason why it is inadvisable to mix household chemicals at random.

Hypochlorous acid should be stored in a sealed container in a cool dry place out of the reach of children and pets. It is a good idea to mark the container to make sure that people are aware of the contents, and to add a warning that it should not be used with acids.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon1004277 — On Jan 04, 2021

Author is incorrect. Hypochlorous acid is not bleach. Hypochlorite is. He needs to remove this article or learn before writing.

By anon1003829 — On Sep 15, 2020

Please do your research. There is a difference between Hypochlorous acid and hypochlorite (bleach)

Hypchlorous acid is very safe to use. Infact they use it in your grocery store vegetable and fruits. It’s also used in eyedrops as someone stated and also in dentistry. You’re article gives it a bad impression. I would prefer to use Hypochlorous acid versus hypochlorite.

By anon1003300 — On Jun 12, 2020

One would get the impression from this article that HOCL is dangerous. This is misleading given that in its typical use, it is so safe that it is used for wound care and eye treatment.

By anon997663 — On Feb 10, 2017

OCL has many different strengths and is non-toxic and non-chemical based at most consumer levels.

By anon965839 — On Aug 14, 2014

To the other comments, obviously toxicity is often related to concentration. Very dilute hypochlorous acid is not particularly dangerous to people. From what I've read, nor is a 'slightly' acidified bleach solution (as the article seems to acknowledge with it's pH note!). But of course, that would most definitely be "at your own risk".

One must know what they're doing, and take every precaution against accidentally mixing concentrates, lowering the pH too much or trying to acidify strong solutions. Most folks should always follow the instructions for their particular application. There IS such thing as being too casual with things like this.

By the way, technically, chlorine bleach contains the salt of hypochlorous acid, hypochlorite.

By anon296847 — On Oct 13, 2012

Hypochlorous Acid is the active ingredient in Vetericyn a product for skin and wound care for animals. Vetericyn has a website and lists ingredients, etc.

By anon246517 — On Feb 09, 2012

This article states this substance is toxic to people and animals, and should not be ingested.

How is this statement true if my body produces the chemical naturally?

By lonelygod — On Jun 06, 2011

I find it interesting that if you have ever been swimming in a pool, that you've probably taken a dip in some hypochlorous acid.

For myself, the chlorine in pools, which uses hypochlorous acid to kill all the nasty things, has always given me bright red eyes and an uncomfortable sensation on my skin. I can only go swimming in a pool that uses chlorine if I wear swim goggles and take a shower right after.

Does anyone else find that the smell of chlorine in pools makes you a bit light headed?

I have always wondered if this is normal, or if I am just overly sensitive to the chemicals in the water.

By popcorn — On Jun 05, 2011

If you are using a cleaning product that contains hypochlorous acid, such as household bleach, don't mix it with anything, except for water. There are a lot of people out there that mix bleach with vinegar, thinking that they are making a better cleaner.

While adding vinegar to bleach does lower it's PH value, causing it to become a great disinfectant, you also create a lot of extra chlorine gas.

This chlorine gas can be very dangerous, especially in a poorly ventilated area. While you may just experience watery eyes and a sore throat, younger people in your family may have more serious reactions. It is best just not to mix chemicals.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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