Question
Asked 17th Dec, 2012

Why is 70% ethanol used for wiping microbiological working areas?

Why not 100% ethanol or methanol? Can anyone explain the mechanism of action?

Most recent answer

3rd Apr, 2022
Phil Geis
GMQ
Can you provide data supporting your water activity (Aw) concept?

Popular Answers (1)

17th Dec, 2012
Amir Haider
University of Karachi
Dear Riyazulla,
70% percent of alcohol is ideal to a stronger solution. Pure alcohol coagulates protein in contact. Suppose the pure alcohol is poured over a single celled organism. The alcohol will go through the cell wall of the organism in all direction, coagulating the protein just inside the cell wall. The ring of the coagulated protein would then stop the alcohol from penetrating farther from the cell, and no more coagulation would take place. At this time the cell would become inactive but not dead. Under the favorable conditions the cell would then begin to function. If 70 percent of alcohol is poured to a single celled organism, the diluted alcohol also coagulates the protein, but at a slower rate, so that it penetrates all the way through the cell before coagulation can block it. Then the entire cell is coagulated and the organism dies.
Regards
Amir
126 Recommendations

All Answers (48)

17th Dec, 2012
Nadine A. Gund
G-RS
Hi,
a) 70% ethanol has been found to be most effective in killing microbes. Higher or lower concentrations are not so effective in killing microbes.
b) if you use 90% or absolute ethanol, it will evaporate fast and may not be much effective.
Cheers, Nadine
11 Recommendations
17th Dec, 2012
Amir Haider
University of Karachi
Dear Riyazulla,
70% percent of alcohol is ideal to a stronger solution. Pure alcohol coagulates protein in contact. Suppose the pure alcohol is poured over a single celled organism. The alcohol will go through the cell wall of the organism in all direction, coagulating the protein just inside the cell wall. The ring of the coagulated protein would then stop the alcohol from penetrating farther from the cell, and no more coagulation would take place. At this time the cell would become inactive but not dead. Under the favorable conditions the cell would then begin to function. If 70 percent of alcohol is poured to a single celled organism, the diluted alcohol also coagulates the protein, but at a slower rate, so that it penetrates all the way through the cell before coagulation can block it. Then the entire cell is coagulated and the organism dies.
Regards
Amir
126 Recommendations
17th Dec, 2012
Simon Drescher
Phospholipid Research Center Heidelberg
Hello!
The effectivity of ethanol as e.g. desinfectant or antiseptic agent depends on the concentration of ethanol-water-mixture: An ethanol percentage of 50-80% destroys the cell wall/membrane of bacteria by denaturing their proteins and dissolving their lipids (effective against most bacteria, fungi and some viruses; ineffective against bacterial spores). Therefore, the ethanol has to pass the bacterial membrane/wall to get into the bacteria - if you use 100% ethanol instead, the bacteria get 'sealed' and they will survive... An other mechanism is the high osmotic pressure of ethanol/water-mixtures; and the 70% has the highest one.
Regards.
Simon
39 Recommendations
17th Dec, 2012
Riyazulla Azeez
University of Madras
Thanks all for your valuable suggestion thank you once again
3rd Dec, 2014
Xiaohua Wuke
Fourth Military Medical University
But why not 75%, which is used more commonly in hospital
1 Recommendation
2nd Feb, 2015
Tharaka Darshana Wijerathne
Western University of Health Sciences
Methanol is too much toxic to us. So not used I think. 
1 Recommendation
24th May, 2015
Asghar Estaji
University of Mohaghegh Ardabili
b) 90% ethanolwill evaporate fast
c) An ethanol percentage of 50-80% destroys the cell wall/membrane of bacteria by denaturing their proteins and dissolving their lipids. Effective against most bacteria, fungi and some viruses; ineffective against bacterial spores. Therefore, the ethanol has to pass the bacterial membrane/wall to get into the bacteria - if you use 100% ethanol instead, the bacteria get 'sealed' and they will survive... Another mechanism is the high osmotic pressure of ethanol/water-mixtures; and the 70% has the highest one.
d) Less expensive
e) Safer flammability level
3 Recommendations
25th May, 2015
Pwaveno H. Bamaiyi
University of Jos
 Many colleagues have already pointed the importance of using between 50%-80% Ethanol instead of using 100%. I will just add that the percentage is a product of research on the best percentage dilution of ethanol with water for killing pathogens because 100% ethanol is not very effective. As Xiaohua Wuke question, yes some hospitals use 75% and there are usually variations in the percentage but all are likely to fall within the 50%-80% range.
4 Recommendations
17th Apr, 2016
Tim Sandle
The University of Manchester
70% is more effective against mycobacteria - Best, M., Sattar, S.A., Springthorpe, V.S. et al. Comparative mycobactericidal efficacy of chemical disinfectants in suspension and carrier tests. Appl Environ Microbiol., 1988; 54: 2856–8
5 Recommendations
26th Jul, 2016
Elijah Nya
Akwa Ibom State University
70% alcohol has been found to effective in sterilizing lab bench work area, killing microbes and other contaminants. Its mode of operation is by cell protein denaturation, destruction of cell wall/membrane of the microbes in question as it slowly permeate into cell thereby inhibiting its growth. important is the high osmotic pressure of 70% alcohol than its highest concentration (100%) or lower form. cheers.
2 Recommendations
4th Nov, 2016
Tim Sandle
The University of Manchester
Methanol is not particularly effective at killing bacteria, compared with ethanol. In addition, IPA (iso-propyl alcohol) is generally more effective than ethanol. The following article may be of interest: http://www.americanpharmaceuticalreview.com/Featured-Articles/184449-Pharmaceutical-Facility-Sanitization-Best-Practices-Considered/
6 Recommendations
9th Mar, 2017
Guilherme Arantes Pedro
University of São Paulo
Amir Haider, could you recommend some article with this mechanism
14th Nov, 2017
Caryn L Campbell
Los Angeles Pierce College
let's not forget to mention that the 70% (+/-)alcohol is only effective on the vegetative cell, not the endospore or spore .
2 Recommendations
29th Mar, 2018
NURHIDAYU MOHD SOBRI
University Malaysia Sarawak
Hye, but then how about the effect of volume alcohol and contact time on bacterial growth? For instance 70% alcohol pad/swab product apply on skin before injection.
6th Jul, 2018
Xiurong xu
Northwest A & F University
the 70% (+/-)alcohol is only effective on the vegetative cell, then what is effective on the endospore or spore?
2 Recommendations
2nd Aug, 2018
Ali Bustan Mohsen Al Waaly
University of Al-Qadisiyah
70% ethanol is the minimum concentration when used in a lab setting for aseptic technique. You don't want to go lower, because it will not kill the microorganisms you are trying to kill.
1 Recommendation
8th Sep, 2018
Sumit Kale
Maharashtra State Seeds Corporation Ltd. Akola
Commonly, 70% ethanol is use to wipe bacteria infected place/platform for maintain aseptic/sterile condition. Because, 70% ethanol will affect the cell wall of bacteria as well as affect the growth and multiplication strongly. Also one of reason is ethanol and water combination will create osmotic pressure.
1 Recommendation
21st Oct, 2018
Saleh Alkarim
King Abdulaziz University
Hello
If you are using it for cleaning , then the 70% is so that there is a dehydration effect on the bacteria, thus killing the bacteria.
Good Luck
22nd Oct, 2018
Muhammad Samie
Khyber Medical University
Agreed with all answers however one thing I want to add is the contact time which is required for alcohol to kill the cell. If we use 100% alcohol it will evaporate quickly so the time required for alcohol to show its effect will be reduced, similarly for diluted one the contact time will be increased but the minimum toxic concentration which is required for cell death will not be achieved. hence at 70% we get the best results.
Muhammad Samie
4 Recommendations
28th Oct, 2018
Awanish Kumar
National Institute of Technology Raipur
Because 70% ethanol is bactericidal. This concentration of ethanol able to kill most of the microbes in short time.
21st May, 2019
Ron Hrstka
Mayo Clinic - Rochester
Quite simply, 70% empirically was determined to be the most effective.
1 Recommendation
30th Jul, 2019
Ron Hrstka
Mayo Clinic - Rochester
"70% ethanol is the minimum concentration when used in a lab setting for aseptic technique. You don't want to go lower, because it will not kill the microorganisms you are trying to kill."
70% is not the minimal. It is the optimal.
1 Recommendation
3rd Mar, 2020
Falak Niaz
Khyber Medical University
Also keep this in mind high concentration can also damage the skin so cannot be used as antiseptic for living tissue.
3rd Mar, 2020
Ron Hrstka
Mayo Clinic - Rochester
Autoclaving and high intensity UV lights also should not be used for living tissue.
11th Mar, 2020
Michael h Hayman
AOL
Impossible to get 100 percent ethanol It absorbs water from air 90 percent is possible without elaborate packaging
11th Mar, 2020
Tomáš Hluska
Nagoya University
Michael h Hayman standard is 96% ethanol as that is the concentration when ethanol-water form azeotrope. But 100% ethanol may be achieved through various means.
12th Mar, 2020
Clarissa Kruger
University of Johannesburg
Years ago, it was explained to me very simply... The alcohol denatures the lipids in the cell wall - basically poking holes in the microorganism. The 30% water can then enter, and lyse, the cell. It's like when your nose bleeds on clothes, plain water will make the cells burst, but if you make a saline solution, the cells will wash off the fabric, in tact. That's how I explain it to non-scientists :)
4 Recommendations
16th Mar, 2020
Zafar Iqbal
Pakistan Council of Scientific and Industrial Research
yes, this is all true, but every one should be careful during formulation, time of contact is important, how much it takes time to kill, 70-75% ethanol with layer creating material is suitable.
1 Recommendation
19th Mar, 2020
Gajanan Inamdar
The University of Arizona
Concentrations above 20% alcohol are sufficient to show the cidal effect. The question is duration in which this happens effectively.
1 Recommendation
29th Mar, 2020
Subhash C. Juneja
it precipitates protein and DNA of microorganism, and hence can kill microorganism, just like we use alcohol in protein isolation and DNA isolation procedures
1 Recommendation
30th Mar, 2020
Izzettin Hatip-Al-khatib
Pamukkale University
Ethanol at 70% can dissolve the lipid cover, pass through and disintegrate the proteinous structure. Lower conc. inadequate to dissolve the lipid, higher conc. coagulates the proteinaceous cover and prevents ethanol from disturbing MO RNA/DNA. This is important in case of virions (SARS-Cov-2) with thick lipid coat. Also to correct the erroneous consideration that colognes are disinfectant because the highest degree cologne is 80 degree, which means 40% ethanol
3 Recommendations
6th Apr, 2020
Md. Anowar Hossain
University of Rajshahi
70 percentage ethanol is good for inactivating the SARS-Cov_2. But in Bangladesh Absolute ethanol (99.9 Per) is difficult to find. Really they are not like absolute. May be 95-96 per. Therefore when we prepare the hand sanitizer, pls consider this point. Wish you good health during this emergency period of nCovid-19.
3 Recommendations
15th Apr, 2020
Patrick Were
Kenyatta University
Ethyl alcohol is indeed virucidal against both lipophilic and hydrophilic viruses. Max potency occurs at 70%
2 Recommendations
20th Apr, 2020
Sergio Delarcina-Junior
Clarivate Analytics
All the explanations are possible, but nobody did show a scientific assay for the declarations.
5 Recommendations
9th May, 2020
Anas Alobaidi
Kadir Has University
agree with Md. Anowar Hossain
1 Recommendation
16th Jul, 2020
Prasad D.K.V
NRI Institute of Medical Sciences,
I accept Amir
1 Recommendation
24th Sep, 2020
Sebastian Wojciech Przemieniecki
University of Warmia and Mazury in Olsztyn
Ethanol poorly migrates inside the cell. Due to the properties of the "dipole" called H2O, this migration is improved.
Short-term exposure of bacteria to ethanol will cause only its surface (protein, lipids) to denature and create a protective layer, ethanol will rapidly evaporate and bacteria will rebuild the cell wall.
In addition, ethanol is more expensive than water, nevertheless- concentration less than 60% (ethanol / water) does not work satisfactorily.
Summarizing:
- water increases ethanol migration inside the cell,
- water reduces evaporation of the disinfectant,
- 70% of the agent is cheaper to produce than 99%
16th Oct, 2020
Fatima Javeria
Muhammad Nawaz Shareef University of Agriculture
100% ethanol completely coagulate the outer cells proteins and it works as defense mechanism in the cells of organism but in case of 70% ethanol, the ethanol does not completely coagulates the proteins of the cell hence penetrates in the organisms body and it dies. So the area becomes contamination free.
17th Dec, 2020
Inderpal Singh
Bioinfores.
Because 100 pc ethanol is highly volatile and thus is lost rapidly where as the 70 pc ethanol can retain for little longer and is enough to alter the osmoticum of bacterial cell wall/membrane..
1 Recommendation
29th Jan, 2021
Dina Yousif Mohammed
Al-Mustansiriya University
at70%concentration the ethanol does not evaporate quickly comparing with it at 100% so that give alcoholic enough time to enter the microorganism and destruction cell and that lead to kill
2 Recommendations
14th Feb, 2021
Gabriella Braun
Tel Aviv University
And what about the disinfectant efficacy and usage of 20% ethanol?
From CDC
"Their (ethyl alcohol and isopropyl alcohol ) cidal activity drops sharply when diluted below 50% concentration, and the optimum bactericidal concentration is 60%–90% solutions in water (volume/volume)."
However you can buy it and was also suggested by some people to use it instead of 70% ethanol in cell culture work.
22nd Jul, 2021
Mahipal Shekhawat
Kanchi Mamunivar Government Institute for Postgraduate Studies and Research
This concentration can kill almost all types of microbes present on the surface area.
25th Jul, 2021
Salar Kadhum Ali
Universiti Putra Malaysia
Dear Riyazulla Azeez and all respected colleagues,
The question was crystal clear, he questioned about sanitizing the working area NOT the mechanism or microbicidal activity of the ethanol if I'm not mistaken. As we know, 80-100% of ethanol evaporates quickly and that might be not enough to eradicate all microorganisms on the working place. While lesser concentration needs a longer time to evaporate since in the Lab we are in a rush to do this and that and must assure that the working surfaces are sanitized well to perform other Lab works. So 70% is just perfect to kill all microbes and saving time.
2nd Sep, 2021
Phil Geis
GMQ
Primary efficacy of ethyl (and isopropyl) alcohol is thought to be a function of nonspecific denaturation/coagulation of protein, not dehydration per se and efficacy is established in tens of seconds or less. An essential element is cleanliness of the surface. Alcohol efficacy diminishes greatly on soiled surfaces.
Methanol is much inferior to ethyl and isopropyl alcohols for disinfection. Superior efficacy at 70% (+/-) is empirical =and though to be a matter of penetration and solvency.
Tilley FW, Schaffer JM. Relation between the chemical constitution and germicidal activity of the monohydric alcohols and phenols. J. Bacteriol. 1926;12:303-9.
Morton HE. The relationship of concentration and germicidal efficiency of ethyl alcohol. Ann N.Y. Acad. Sci. 1950;53:191-96.
see chapters on alcohol as disinfectant Block's books - the latest.
McDonnell, G., 2020. Block’s Disinfection, Sterilization, and Preservation. Lippincott Williams & Wilkins.
1 Recommendation
2nd Apr, 2022
Owolabi Oluwafemi Akinkunmi
Osun State College of Technology, Esa Oke.
This have to do with water activity. At 70%, Ethanol tend to be better compared to 90% because the water helps the disinfectant to stay longer on the bacteria cell, thus giving it more time to interact/Disrupt normal 'Life' process of the bacteria

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