In May 2021 we undertook a study to compare the efficacy of our hypochlorous acid with two other products that are currently on the market and claiming to be HOCl; putting different hypochlorous acid brands to the test against our HOCl brand Salvesan.
The aim of the study was to ascertain the efficacy of three HOCl based products under “real life use” conditions. Efficacy was measured by examining pre and post treatment levels of surface micro bioburden. Each HOCl product was be tested under the same conditions.
Hypochlorous acid is produced by the mammalian body in response to invading pathogens. It is extremely fast acting (eg 12 milliseconds to kill E. coli), effective against a wide range of pathogens (bacteria, viruses, yeasts, moulds, fungi etc.) and does not harm mammalian cells. The fast acting, broad spectrum activity of HOCl make it an ideal disinfectant.
Hypochlorous acid is made through electrodialysis of a saline solution. The resulting HOCl can be anything from 65-99.9% pure depending on the type of electrodialysis cell used and the input materials. Aqualution Systems has been working with HOCl for nearly 20 years using cells that we have developed and refined. Our generating systems are used in a range of industrial settings from primary agriculture (keeping animal drinking water clean) to food factories (ensuring our food is bacterially and virally decontaminated). HOCl solution is extremely effective at killing pathogens, but HOCl is unstable and the shelf life is around 48-72 hours, depending on storage conditions. Aqualution has been the only company to successfully stabilise HOCl and sell the stable product into a range of markets including healthcare, facilities management, pet care, veterinary care, dental surgeries and consumer products. Our infection control product is called Salvesan and used in this study. Aqualution products are fully compliant with the Biocidal Products Regulation (EU 528/2012) and are the dossier holders for hypochlorous acid.
There are many HOCl products that are being marketed in the UK. Many of these products do not comply with the BPR in the EU or the UK. Furthermore our by putting different hypochlorous acid brands to the test we have shown that the amount of free chlorine in the products is hugely variable. Either it is very high or absent. This is due to the differences between electrodialysis cells and resultant purity / stability of the HOCl produced. Additionally there are some companies whose products are just acidified bleach, despite being marketed as HOCl.
Methodology
Sheets of lino with eight sampling tiles marked out (all 10cm x 10cm) were deliberately contaminated and left to air dry (approximately 30 minutes): each tile had one squirt of contaminated liquid sprayed on it (approximately 1.5ml). One sheet of lino was used for each HOCl product. Two random tiles were chosen on each lino sheet. The contaminated sheet was placed at desk height in preparation for treatment and the two tiles were swabbed prior to the treatment. Tiles were sprayed with the designated HOCl product, immediately wiped with kitchen towel and post-treatment swab samples were taken. Swabs were couriered to the lab the same day (One Scientific, Avonmouth) where they were analysed for aerobic colony counts (ACC).
Products analysed
The different hypochlorous acid products put to the test are listed below. The brands have not been named in this trial:
| Product | Free available chlorine | pH |
| 1. Salvesan | 140 | 7.2 |
| 2. Another HOCl brand sold online | 265 | 6.3 |
| 3. Another HOCl brand sold online and in high street retailers | 75 | 6.2 |
Results
All swabs were successfully analysed. Results for each product are presented in the following table. All results are presented as colony forming units per swab (cfu/swab).
| Tile # | Product | cfu/swab | Log | Reduction | |||
| Pre | Post | Pre | Post | Log | % | ||
| 1 | Salvesan | >10,000,000 | <10 | 7 | 0 | 7 | 99.99999 |
| 2 | Salvesan | >10,000,000 | 10 | 7 | 1 | 6 | 99.9999 |
| 3 | Product 2 | >10,000,000 | 400,000 | 7 | 5 | 3 | 99.9 |
| 4 | Product 2 | >10,000,000 | 150,000 | 7 | 5 | 3 | 99.9 |
| 5 | Product 3 | >10,000,000 | 9,000 | 7 | 3 | 4 | 99.99 |
| 6 | Product 3 | >10,000,000 | 1,000,000 | 7 | 6 | 1 | 90 |
The total number of bacteria recovered on each tile prior to the spray and wipe treatment was >10,000,000 which was reduced
for all treatments. Reductions were very variable: the best results were achieved by Salvesan with 6 and 7 log reductions observed. This means that 99.9999% and 99.99999% of bacteria were removed.
Product 2 gave consistent 3 log reductions (99.9% bacteria removed).
Product 3 achieved one good result and one poor result (4 logs/ 99.99% and 1 log/ 90% reduction).
When looking at percentage reductions it is easy to think that there is not much difference between a 3 log (99.9%) reduction and a 6 log (99.9999%) reduction. However the table below illustrates the differences between the different logs when a start number of 1,000,000 is used:
| Start count | Log reduction | % reduction | Bacteria left |
| 1,000,000 | 1 | 90 | 100,000 |
| 1,000,000 | 2 | 99 | 10,000 |
| 1,000,000 | 3 | 99.9 | 1,000 |
| 1,000,000 | 4 | 99.99 | 100 |
| 1,000,000 | 5 | 99.999 | 10 |
| 1,000,000 | 6 | 99.9999 | 1 |
| 1,000,000 | 7 | 99.99999 | – |
Achieving a 4 log reduction (99.99%) sounds very impressive. However, if you used the product on a surface which had 1,000,000 bacterial colonies on it, you would still be left with 100 bacterial colonies after you had disinfected it.
All three products achieved reductions when used as a spray and wipe on a contaminated surface. However, the efficacy varied greatly between the HOCl products with Salvesan being the best.
If you would like any different hypochlorous acid brands put to the test please get in touch.
