Appliance of Science: Which is better, liquid soap or a bar of soap?

With Covid 19 on everyone’s minds at the moment, we are all intent on keeping our hands clean. But what is the best type of soap to choose, or does it matter? Dr Naomi Lavelle has the answers.

Appliance of Science: Which is better, liquid soap or a bar of soap?

With Covid 19 on everyone’s minds at the moment, we are all intent on keeping our hands clean. But what is the best type of soap to choose, or does it matter? Dr Naomi Lavelle has the answers.

What exactly does soap do?

Soap is pretty good at what it does, which is cleaning our hands. It does this because it is made up of molecules that have a lipid or oil loving part on one end and a water loving part on the other. The microbes (bacteria and viruses) on our hands are held in place with dirt and oils. So the oil loving part of the soap molecules sticks to the dirt and oils on our hands, surrounding them and lifting them from the skin. This creates little parcels but they still need to be removed from our hands. This happens when the other end of the soap molecules, the water loving parts, stick to the water molecules and therefore allow the dirt and microbes to be washed away.

Bar versus liquid

Bars of soap and soap dispensers are equally effective when washing your hands.
Bars of soap and soap dispensers are equally effective when washing your hands.

Both liquid soap and bar soap have been shown to be equally as efficient in washing our hands. Although germs may stay on a bar of soap between washing, studies have consistently shown that this does not impact the efficiency of the soap. Depending on how the soap is used, some studies suggest that a liquid soap dispenser is preferable for use in high volume areas (public toilets) while others report that these liquid soaps pose a greater contamination risk through change or refill of the dispenser. From an environmental point of view, the bar of soap is the overall winner.

What about water temperature?

Washing our hands in water alone will not efficiently remove all microorganisms but water is necessary to correctly wash our hands; It helps to lather the soap, disperse it around the skin and to rinse away the germs. Warm water may do a slightly better job of lathering the soap but water temperature has not been shown to increase the removal of germs when hand washing. We can still wash our hands correctly with cold water.

Should we choose antibacterial soap?

Antibacterial soap is regular soap (detergent) with some additional ingredients. These ingredients are primarily targeted at killing most bacteria. The detergent/soap element is actually the most effective part for removing viruses. There is no evidence to suggest that the detergent effect of soaps is improved by the addition of antibacterial material.

Overuse of antibacterial soaps can potentially add to the problem of antibiotic resistance in bacteria.

How about alcohol?

Alcohol can kill viruses, but only at high concentrations of 60 percent or higher (regular vodka and whiskey, for example, only contains 40 percent alcohol). In general, alcohol containing cleaning products are better suited to use on surfaces, not skin.

Alcohol based hand gels are often more gentle on the skin than hand-sanitising products
Alcohol based hand gels are often more gentle on the skin than hand-sanitising products

Alcohol-based hand gels usually contain emollients, as well as having a high alcohol content (60 to 70 percent) and these are more gentle on the skin. These can be effective in killing viruses and do not pose a problem for antibiotic resistance. Alcohol-based hand sanitisers can be less effective on hands that are excessively dirty or oily.

The best way to use these products is to ensure you add enough (approximately three millilitres) to the palms of your hands, and then rub thoroughly over the skin, for about ten to 15 seconds.

    Useful information
  • The HSE have developed an information pack on how to protect yourself and others from coronavirus. Read it here
  • Anyone with symptoms of coronavirus who has been in close contact with a confirmed case in the last 14 days should isolate themselves from other people - this means going into a different, well-ventilated room alone, with a phone; phone their GP, or emergency department - if this is not possible, phone 112 or 999 and in a medical emergency (if you have severe symptoms) phone 112 or 999

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