Is handwashing with ash safe? - Does it kill any viruses?


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  • goeco
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Re: Is handwashing with ash safe? - Does it kill any viruses?

Hi Elisabeth,

sodium hydroxide is caustic soda or lye. Lye dissolves greases. White wood ash contains potassium carbonate, or potash, along with calcium hydroxide, but very little if any sodium hydroxide. By adding water to white wood ash, the calcium hydroxide and potassium carbonate react, forming caustic potash (ash lye, potassium hydroxide) and calcium carbonate (please somebody correct me if I'm wrong, I'm not a chemist!).

On this basis I have always assumed that handwashing with ash and water means handwashing with ash lye. I wash my hands with wood ash, which is particularly effective at removing greases and hard-to-remove dirt. Ash will remove just about anything from hands, and it certainly is not painful to use and it doesn't burn skin. Well, not mine anyway...

I'm asking whether it's appropriate for people from the developed world who like the smell and feel of soap to impose their paradigms on those with different practices...  Habits are also influenced by tradition and availability. If someone washes their hands effectively with wood ash and has always done so, because they are happy with that practice and use their own resources, is it right for someone to come along and say "you should use soap, it will feel nice on your skin and make you smell nice."?

Dean Satchell, M For. Sc.
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  • sianwhite
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Re: Is handwashing with ash safe? - Does it kill any viruses?


The statement in our post that says 'Be aware that handwashing with ash does not feel very nice and does not leave hands feeling and smelling nice in the way that soap does, as such promoting ash may actually discourage people from practicing handwashing' is based on research that I and others have done in several countries exploring soap products and ash. This includes work done in DRC, Ethiopia, and Nigeria - all settings where ash is commonly promoted by NGOs and quite widely used in some regions. This sentiment reflects the sentiment of populations who, across these countries, consistently rank ash as the least desirable option for handwashing. The fact that it continues to be used widely is much more a factor of poverty and inequality. In fact people often directly said that ash is perceived as something only poor people would use - a label that understandably they did not wanted to be associated with.

In general I am not familiar with organisations promoting the use of soap and discouraging the use of ash. In most cases handwashing with soap is promoted and organisations explain that if soap is scarce ash can be used instead. However at the moment I think this is an imperative to actively encourage people to use soap where possible because we know that it can effectively destroy and remove SARS-CoV-2 from hands. While it is plausible that ash may be able to do the same we have no evidence to suggest this at the current time.

I hope that helps

Sian White

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Environmental Health Group - Faculty of Infectious and Tropical Diseases London School of Hygiene and Tropical Medicine

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  • Chaiwe
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Re: Is handwashing with ash safe? - Does it kill any viruses?

This has been an interesting thread to read.

Allow me to add that quite a good number of people in urban communities use soap either in its liquid or solid form, However, many communities in rural areas can not access or afford soap. The SAGE journal documents some research on handwashing practices in Bangladesh and elsewhere have actually shown that ash can be a low-cost alternative to soap. Bangladeshi fieldwork carried out in 2007 found that 13% of people in the sample used ash or soil (which brings about a whole other discussion) to wash their hands after defecating, compared to 19% who used soap. Organizations like UNICEF have recommended that people without soap wash their hands with ash. The Cochrane Library early this year in April did a study to know whether people who use ash for hand cleaning were more or unlikely to catch infections than people who use soap. The study investigated children who had been to the hospital with diarrhoea compared with children who had not. The study focused on handwashing in children. Most families that used ash for hand cleaning made a similar number of hospital visits for children with diarrhoea as those families that used soap. 

Traditionally within the African setting, soil, ash, and salt have been used as both mechanical and chemical forms of neutralizing contaminants on dirty hands and surfaces.   The premise of the effectiveness of such materials assumes that households will obtain the soil, ash, and salt from uncontaminated sources.  The availability of these alternative methods may be limited to people living in informal urban settlements areas but not in rural areas.

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  • KellyKBaker
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Re: Is handwashing with ash safe? - Does it kill any viruses?

I am glad to see this topic come up. I conducted the research in a paper cited earlier in this thread where we examined whether the likelihood of diarrhea was different for households relying on soap versus ash:

Title: Association between Moderate-to-Severe Diarrhea in Young Children in the Global Enteric Multicenter Study (GEMS) and Types of
Handwashing Materials Used by Caretakers in Mirzapur, Bangladesh. 
Authors: Baker, K.K., Dil Farzana, F., Ferdous, F., Ahmed, S., Kumar Das, S., Faruque, A.S.G., Nasrin, D., Kotloff, K.L., Nataro, J.P., Kolappaswamy, K., Levine, M.M.,
Year: 2014.
Am. J. Trop. Med. Hyg. 91, 181–189.

One piece of data that gets overlooked in that paper is that the epi data was followed up with environmental microbiology bench experiments where i prepared an ash and water suspension as described by Bangladeshi women and then spiked it with different types of bacterial pathogens, like Shigella, Vibrio cholera, and ETEC. I was able to isolate a handful of pathogenic bacteria in high dose bacteria concentrations out to 15 or 20 seconds, but nothing (including high pH loving vibrios!) survived for longer time points. As proposed earlier, the pH 9-10 of such a solution is so caustic that bacteria generally cannot survive. It destroys the lipid structure in the cell wall.

Given what we know about the survival of many viruses in the environment, it is reasonable to hypothesize that yes ash is fairly effective at destroying viruses or the molecular binding structures on their surfaces as well. Maybe I can motivate a student to repeat some of those experiments with the viruses we have in house...

That does not make it pleasant or ideal to wash with, or mitigate the chemical exposure issues, so I endorse the strategies that recommend it in situations where washing might not happen at all, or with water only.

Post-comment edit
To my knowledge the majority of ash users are rural, as noted by a previous author, and the sources are wood, brush, and cow dung. Exposure to man-made chemicals, lead, etc from such burn sources seems very unlikely.
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Re: Is handwashing with ash safe? - Does it kill any viruses?

washing with ash removes dirt, oil, and grease which removes almost 90% of bacteria. moreover, it would be useful if you are not dealing in an area full of harmful bacteria and viruses as it doesn't pollute water as much as soap does. 
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