ClO2 vs HOCl

What is the difference between hypochlorous acid (HOCl) and chlorine dioxide (ClO2)?

Chlorine dioxide is a compound of chlorine (Cl) and oxygen (O₂). The names and scientific formulas of hypochlorous acid and chlorine dioxide may look similar, but they are two fundamentally different substances.

What is Chlorine Dioxide (ClO₂)?

Chlorine dioxide is a chemical compound with the formula ClO₂. It is a yellow-green, sharp-smelling gaseous substance often used as a disinfectant and bleaching agent. Chlorine dioxide is effective against a wide range of microorganisms, including bacteria, viruses, and fungi. It is commonly used in water treatment to purify and disinfect water, as well as in the food industry to disinfect surfaces. ClO₂ can cause irritation in the nose, throat, and lungs when inhaled. Exposure to high concentrations can lead to shortness of breath due to damage to substances in the blood that transport oxygen [1].

What is Hypochlorous Acid (HOCl)?

Hypochlorous acid (HOCl) has mild yet powerful disinfecting properties. Like ClO₂, HOCl is also an oxidizing agent that effectively eliminates a wide range of bacteria, viruses, fungi, and yeasts and removes biofilm from surfaces. HOCl is produced using three simple ingredients: water, salt, and electricity [2]. Through the process of electrolysis, HOCl is formed, resulting in a disinfectant with HOCl as the active ingredient, which we call Watter WDS (Watter Disinfection Solution).

What are the advantages of HOCl over ClO₂?

Hypochlorous acid (HOCl) has several advantages over chlorine dioxide (ClO₂), particularly in terms of safety, effectiveness, and ease of use. HOCl is effective against bacteria and viruses in low concentrations. It acts quickly because it is neutrally charged and can easily penetrate cell membranes. Additionally, HOCl can be produced on-site, ensuring it is always applied fresh. ClO₂, on the other hand, often requires higher concentrations and may form harmful residues such as chlorates. ClO₂ can remain relatively stable in aqueous solutions, but in gaseous form, it is very unstable and even explosive at higher concentrations [3].

See the table below for a more detailed overview of the differences between HOCl and ClO₂:

	Hypochlorous Acid	Chloordioxide
Scientific Formula	HOCl	ClO2
Production	Electrolysis of water and salt	Door een chemische reactie van natriumchloriet met natriumbisulfaat
Kleur	Transparent	Yellow
Efficacy	Uiterst effectief tegen: Bacteriën Virussen Schimmels/gisten	Lagere effectiviteit dan HOCl in dezelfde concentraties, met name tegen gisten/schimmels
Bijeffecten	Hypoallergenic and gentle to the skin	Toxic if inhaled, explosive
Warning Symbols	N/A