HOCl Trust for Hygiene and Safer Water

HOCl - "...the gold standard by which all antiviral, antibacterial and sporicidal agents must now be compared.”

Dr. Joe Selkon, MBChB, FRCPath, DCP.

Formerly Consultant Microbiologist, Oxford University John Radcliffe Hospital 10th March 2010

Image source: histmodbiomed.org

Relevant Scientific Data and Technical Information

Sodium Dichloroisocyanurate (NaDCC)

Chlorine Release

Solutions of NaDCC release "free" available chlorine (av.Cl2) in the form of HOCl (Hypochlorous acid) and OCl (Hypochlorite), in 50:50 equilibrium with the "combined" available chlorines, mono- and dichloroisocyanurate. According as the free chlorine becomes used up by micro-organisms and organic matter etc., the combined will release further free av.Cl2 to restore the 50:50 balance.

This will continue with increasing demand until no further chlorine remains available. This is a unique phenomenon among chlorine donor compounds and explains:

  1. The greater biocidal capacity of NaDCC
  2. Why NaDCC is less toxic and less corrosive
  3. Why NaDCC solutions persist for much longer, and in an active state

Lethal Biocide Action

It is generally believed that the antimicrobial activity of NaDCC is due to chlorination of cell protein or enzyme systems by free HOCl, causing hydrolysis of the peptide chains of the micro-organisms' cell membranes.

Effect of pH

pH has probably the greatest influence on the disinfectant activity of all chlorine solutions and the HOCl ion is responsible for the microbiocidal activity of NaDCC solutions. Hypochlorous acid dissociates eventually as follows:- HOCl to H+ + OCl- ; with HOCl possessing 100 times greater potency than OCl (hypochlorites).

This Dissociation of HOCl is critically pH dependent:

At pH5: abt. 99.7 % HOCl is released from solutions of NaDCC. At pH7 (Pure Water): abt. 72.3% At pH 9.5 (average for sodium hypochlorite solutions) a mere 0.19% HOCl is yielded up.

This helps to explain the significant advantage in microbiocidal activity of NaDCC based products over all other chlorine donors.

It is important to remember that:-

NaDCC products are active over a pH range of 5.0 - 6.5.

They differ totally from hypochlorites and chloramines Hypochlorites (bleach) and Chloramines are effective only at alkaline pH (av. 9.5), releasing minimal or relatively low levels of HOCl compared to NaDCC-based compounds.

NaDCC products release highly significant levels of HOCl.

Therefore they are:

  • More effective
  • Less toxic and less corrosive than other chlorine compounds
  • Rapid HOCl release
  • Rapid biocidal activity
  • No skin irritation

Smell: The faint, characteristic "chlorine" smell from all NaDCC solutions is due to the release of chloramines (breakdown products of NaDCC). The scent becomes more pronounced as organic substances like skin, micro-organisms or any organic contamination load come into contact with NaDCC solutions.

Spectrum of Microbiocidal Activity


Actinobacillus sp.

Actinomyces pyogenes

Bacillus anthracis

Brucella abortus

Clostridium butyricum

Clostridium sp.

Corynebacterium sp. Enterobacter cloacae

Enterobacter sp.

Eschericia coli

Escheria coli 0157-H

Erysipelothrix sp

Klebsiella sp.

Legionella pneumophilia Leptospira sp.

Listeria monocytogenes

Mycobacterium paratuberculosis

Mycobacterium smegmatis

Mycobacterium sp.

Mycobacterium terrae 232 Mycobacterium

tuberculosis ATCC25618

Mycoplasma mycoides

Mycoplasma sp.

Norcardia sp.

Pasteurella sp.

Proteus vulgaris

Pseudomonas aeruginosa NCTC6749

Pseudomonas aeureus

Pseudomonas fluorescens IM

Rhodococcus equi.

Salmonella dysenteriae

Salmonella typhimurium

Salmonella typhimurium phage type 104

Salmonella typhosa

Shigella sonnei

Staphylococcus agalactiae

Staphylococcus aureus

Methicillin Resistant Staphylococcus aureus - MRSA

Staphylococcus dysgalactiae

Staphylococcus uberis

Streptococcus equi.

Vibrio sp.


Adeno virus 3,7,7a,8 & 12

Aujesky's virus

Bovine Viral Diarrhoea virus (BVD)


Coxsackie A2 (Purified)

Creutzfeldt-Jakob Disease virus

Distemper virus


Equine Herpes virus (1 & 4)

Equine Influenza virus

Foot & Mouth Disease virus

Hardpad virus

Hepatitis A virus

Hepatitis B virus

Infectious hepatitis virus

Herpes Simplex virus 1

Human Rotavirus

Human Immunodeficiency virus (HIV)

HIV + 10% plasma HIV in contaminated blood

Newcastle Disease virus


Poliovirus 1, 2 & 3

Reovirus 1,2 & 3

Respiratory Syncitial virus (RSV)


Simian Rotavirus SA11 (Purified)

Theiler's virus (Purified)


Bacterial spores:

Bacillus anthracis spores

Bacillus cereus spores

Bacillus globigii spores

Bacillus subtilis spores

Clostridium bifermentans spores

Clostridium butyricum spores

Clostridium histolyticum spores

Clostridium histolyticum spores 503 Clostridium

sporogenes spores

Clostridium tetani spores

Tubercule bacilli spores


Aspergillus fumigatus

Aspergillus niger

Candida albicans

Cryptococcus sp

Fusarium sp

Microsporum sp

Mucor sp Penicillium sp

Saccharomyces sp

Trichophyton sp

Scientific Advisory Panel


Dr. J.B. Selkon - Oxford University and John Radcliffe Hospital

Dr Joe Selkon died in March 2013. However he was fully supportive for the entire duration of our work together on HOCl since 1994. He bequeathed all his personal files to Charles Cocking and requested he continue to use his data to further the research.

Dr. Stephen P. Barrett - Consultant Medical Microbiologist, Department of Medical Microbiology, Imperial College at St. Mary's Hospital, London. Deputy Editor, Journal of Hospital Infection.


Dr. Iwona Beech - B.Sc.Ph.D.C.Chem. Research Professor University of Oklahoma, Department of Microbiology & Plant Biology, GLCH, 770 Van Vleet Oval, Norman, OK 73019, USA.


Dr. Carlton Evans - Imperial College and London School of Hygiene and Tropical Medicine.


Dr. Edwin Prince (retired) - University of Central Lancashire. National Board of Expert Witnesses.



Dr. Martin Fulford - BDS. MPhil. DGDP. FIBMS.


Dr. Hugh Martin - BSc (London), MSc (Imperial), PhD (London), DIC - Royal Agricultural College, Cirencester. Principle Lecturer – Agricultural Science.

Environmental Protection

Dr Ginny Moore - Biosafety Investigation Unit,  Public Health England, Porton Down, Salisbury, Wiltshire.

Selection of Peer Review Papers on HOCl 

1. British Dental Journal 198, 353 - 354 (2005)  Published online: 26 March 2005 | doi:10.1038/sj.bdj.4812174. An investigation of the efficacy of super–oxidised (Optident/Sterilox) water for the disinfection of dental unit water lines.

2. V. Zinkevich, I.B. Beech, R. Tapper, I. Bogdarnia (2000) Journal of Hospital Infection 46: 153-156; The effect of HOCl on Escherichia coli.

3. H. Hays, P.R. Elliker and W.E. Sandine (1966) Applied Microbiology, page 575-581; Microbial Destruction by Low Concentrations of Hypochlorite and lodophor Germicides in Alkaline and Acidified Water. 

4. I.B. Beech, V. Zinkevich, J.A. Sunner, C.C. Gaylarde (2007) Technical Report; Evaluation of the effect of Salvox (Stabilised HOCl) on Planktonic Populations of model marine bacteria: Aerobic slime forming bacterium of the Pseudomonas Genus and anaerobic sulphate-reducing bacterium Desulfovibrio alaskensis. 

5. J.B. Selkon, G.W. Cherry, J.M. Wilson, M.A. Hughes (2006) Evaluation of Hypochlorous Acid washes in the treatment of chronic venous leg ulcers. 

6. N. Shetty, S. Srinivasan, J. Holton, G.L. Ridgway, J.B. Selkon (1997) Evaluation of Microbiocidal activity of a new disinfectant; against vegetative Bacteria, Spores, Candida albicans, Mycobacterium species. 

7. N. Shetty, S. Srinivasan, J. Holton and G.L. Ridgway (1999) Journal of Hospital Infection 41:101-105 Evaluation of microbiocidal activity of a new disinfectant: HOCl against Clostridium difficile spores, Helicobacter pylori, vancomycin resistant Enterococcus species, Candida albicans and several Mycobacterium species.

7. J.B. Selkon, R.B. Babb, R. Morris (1999) Evaluation of the antimicrobial activity of a new super-oxidised water, HOCl for the disinfection of endoscopes. 

8. J.B. Selkon, A. Crossley (2009) Analysis of Hypochlorous Acid. 

9. J. Lorrain Smith, A. Murray Drennan, Theodore Rettie and William Campbell. Experimental Observations on the antiseptic action of Hypochlorous Acid and its application to wound treatment. Br Med J Jul 1915; 2: 129 – 136; doi:10.1136 bmj.2.2847.129. 

10. Wang L, Bassiri M et al. Journal of Burns and Wounds April 11th 2007 pp 65-79. Hypochlorous Acid as a potential wound care agent. 

11. Granum, Magnusson. International journal of food microbiology 1987 page 183-186. The effect of pH on hypochlorite as a disinfectant. 

12. J. Clark, S. P. Barrett, M. Rogers and R. Stapleton. Department of Microbiology, Charing Cross Hospital, London, UK 2 July 2006 Efficacy of super-oxidized water fogging in environmental decontamination.

13. Ramalingam S, Cai B, Wong J, Twomey M, Chen R, Fu RM, Boote T, McCaughan H, Griffiths SJ, Haas JG. Sci Rep. 2018 Sep. 11. Antiviral innate immune response in non-myeloid cells is augmented by chloride ions via an increase in intracellular hypochlorous acid levels.

14. Jeffrey Williams, Eric Rasmussen, Lori Robins October 6, 2017 Infectioncontrol.tips: Hypochlorous Acid: Harnessing an Innate Response

15. Hakimullah HAKIM, Md. Shahin ALAM, Natthanan SANGSRIRATANAKUL, Katsuhiro NAKAJIMA, Minori KITAZAWA, Mari OTA, Chiharu TOYOFUKU, Masashi YAMADA, Chanathip THAMMAKARN, Dany SHOHAM and Kazuaki TAKEHARA . 2016 Jul; 78(7): 1123–1128. Inactivation of bacteria on surfaces by sprayed slightly acidic hypochlorous acid water: in vitro experiments.

16. Geun Woo Park,Deyanna M. Boston,Julie A. Kase,Mark N. Sampson and Mark D. Sobsey. Applied Environmental Microbiology. 2007 Jul. Evaluation of Liquid- and Fog-Based Application of Sterilox Hypochlorous Acid Solution for Surface Inactivation of Human Norovirus.

17. Thomas Clasen, Paul Edmondson. International Journal of Hygiene and Environmental Health 209 (2006) 173–181: Sodium dichloroisocyanurate (NaDCC) tablets as an alternative to sodium hypochlorite for the routine treatment of drinking water at the household level.

18. Anagnostopoulos AG, Rong A, Miller D, Tran AQ, Head T, Lee MC, Lee WW. Dermatologic Surgery 2018 Dec.; 0.01% Hypochlorous Acid as an Alternative Skin Antiseptic: An In Vitro Comparison. 

19. Hakim H, Thammakarn C, Suguro A, Ishida Y, Nakajima K, Kitazawa M, Takehara K. Avian Disases. 2015 Dec.;  Aerosol Disinfection Capacity of Slightly Acidic Hypochlorous Acid Water Towards Newcastle Disease Virus in the Air: An In Vivo Experiment.