Difference between hypochlorous acid water and sodium hypochlorite

On May 29, the National Institute of Technology and Evaluation (NITE) issued an interim report stating that about “hypochlorous acid water” used for the purpose of disinfecting new coronavirus, “its effectiveness has not been confirmed at this time.”

In Japan these days, there are “hypochlorous acid atomizers” as countermeasures against new coronaviruses everywhere. Those who believed that it would be effective against the coronavirus in that space and purchased and used it would have been disappointed at the news. Aside from those who use it just to comfort their mind regardless of the effect.


Virus classification

Here is a review. Virus particles have the following three basic structures.

(A) A type in which virus particles do not have an envelope (outer membrane)

This type includes viruses such as polio virus, adenovirus, and norovirus.


(B) A type in which virus particles have an envelope (outer membrane), but proteins are not attached to nucleic acids

Herpes virus falls into this type.


(C) A type in which virus particles have an envelope (outer membrane) and nucleic acids have proteins

Influenza virus, coronavirus, measles virus, etc. are this type. The new coronavirus this time also falls into this type structurally.



In addition, there are two further categories.

(1) Virus whose nucleic acid is DNA

(2) Virus whose nucleic acid is NA

Influenza virus and norovirus are NA viruses. The new coronavirus this time is also an NA virus.


As you may have noticed here, the particle structures of the novel coronavirus and influenza virus are similar. Therefore, what is effective against influenza virus is also effective against the new coronavirus, and it is speculated that acidic electrolyzed water (hypochlorous acid water) will be effective, leading to the current situation.


Of course, based on that assumption, the Ministry of Economy, Trade and Industry selected the following three fields of products as disinfecting methods and products that could be effective against the new coronavirus, and outsourced the verification test to NITE.

  • Surfactant (Kitchen detergent, etc.)

  • Hypochlorous acid water (generated by electrolysis)

  • Quaternary ammonium salt

The result was the opening interim report on May 29. The effect of hypochlorous acid water could not be confirmed at this time.



The topical “hypochlorous acid water” (electrolyzed water) (HOCl) contains the bactericidal component “hypochlorous acid”, but the effect on the new coronavirus is not confirmed yet. Because it is effective against influenza virus and old type (?) coronavirus, it is used for disinfecting food and articles.

On the other hand, what we often see in your comments is “sodium hypochlorite (soda)” (NaClO). This is also active as a bleaching agent. Sodium hypochlorite solution is very alkaline. Sodium hypochlorite also contains a bactericidal component “hypochlorous acid.”


Difference between hypochlorous acid water and sodium hypochlorite

There are three differences between the two. I will explain each one.

1) Different pH

As I touched briefly in the previous chapter, hypochlorous acid water is weakly acidic, but sodium hypochlorite is a strong alkali.

It is a famous story that a skin is weakly acidic. Hypochlorous acid water has a pH close to that of a skin, so there is less damage to a skin.

The reason your hands are slimy when you touch something alkaline is that your skin is melting due to damage to it. Sodium hypochlorite causes this phenomenon, so application to a skin is strictly prohibited.


2) Different usage

Although hypochlorous acid water is used as it is, sodium hypochlorite is generally diluted before use.

Dilution example (stock solution 12% concentration)

Use Effective chlorine concentration Dilution ratio (example)
Disinfection of water (drinking water, pool, and drainage) Approximately 0.8 ppm Approximately 140,000 times(approximately 0.7 ml for 100 L of water)
Disinfection of tableware Approximately 100 ppm Approximately 1,200 times (approximately 75 ml for 100 L of water)
Disinfection of raw vegetables and fruits Approximately 100 ppm Approximately 1,200 times (approximately 75 ml for 100 L of water)
Disinfection of bathrooms, bathtubs, toilet bowls, etc. Approximately 600 ppm Approximately 200 times (450 ml for 100 L of water)
Stain removal/bleaching (liquor, fruit juice, ink, etc.) 600-2000 ppm 60-200 times (450 to 1,500 ml for 100 L of water)


3) Different form of bactericidal component

Free chlorine contained in hypochlorous acid water is contained in the form of unstable HClO. Therefore, although it has a bactericidal effect even at low concentrations, it decomposes immediately when it comes into contact with organic substances, so a large amount of hypochlorous acid water is required when sterilizing cookware and medical equipment. Even when applying it to your hands, it has been decomposed by the time you spread the hypochlorous acid water applied to your left hand to your right hand, so it is necessary to apply a large amount of hypochlorous acid water directly to both hands.

Since the sodium hypochlorite aqueous solution is alkaline, it contains a large amount of free chlorine in the form of stable ClO-. Being stable, it requires a higher concentration than hypochlorous acid water to produce a bactericidal effect. On the other hand, since it is stable, it has a long-lasting sterilizing effect, so it is used for sterilization such as wiping.




I briefly summarized the difference between hypochlorous acid water and sodium hypochlorite, but there is also “calcium hypochlorite.” It is a solid and is weakly alkaline when dissolved in water.

I think some people in Japan remember that a teacher threw white tablets called “kalki” into a school pool a long time ago. This white tablet is “calcium hypochlorite.”

Kalki is made by absorbing chlorine in calcium hydroxide (lime). This chlorine played a role in suppressing the growth of various bacteria in a pool.

Nowadays, sodium hypochlorite, which is a liquid and easy to manage, has become the mainstream. It is also used for sterilization of tap water. Unlike solid calcium hypochlorite, sodium hypochlorite is a liquid, so it is easy to dissolve in water and its concentration can be adjusted easily.

About disinfection of tap water

Water Supply Act in Japan stipulates that “basically, chlorine should be used to disinfect water.” For tap water, Japan has approved the use of especially 3 substances: “sodium hypochlorite,” “calcium hypochlorite,” and “liquefied chlorine.” Sodium hypochlorite is currently used to sterilize tap water.



The effect of hypochlorous acid water on the new coronavirus is not confirmed yet, but what about sodium hypochlorite? To answer this question, it is stated in the Ministry of Health, Labor and Welfare documents that sodium hypochlorite is effective against the new coronavirus. (Visit the URL below)


However, since it is a strong alkali, it cannot be either applied to a skin or used for hand disinfection. There is also a note on the link above, as you should wear gloves when disinfecting. In addition, it may corrode metals, so I think it is better to use sodium hypochlorite and alcohol properly for disinfection.




We are very happy to share this article with you.

Comments for this article

  • 四方輝夫 より:




    • sankyo管理者 より:



  • 高尾幸江 より:










    • sankyo管理者 より:




We will wait your comments.

Your e-mail address will not be disclosed. , Marked with * are required.

Related articles