The science of soap !!

The current situation with the Corona virus/COVID 19 has brought the importance of good hand washing in to the news, so here’s the science bit.

Soap is a mixture of oil or fat with water and an alkali or basic salt, the process of making soap is called saponification [there’s a great Scrabble word for you !]. We think that the ancient Babylonians were the first people to make soap as archaeologists found their soap recipes carved in to clay containers dating back to 2800 BC. Their soap recipes included animal fats, wood ash and water and their soap was probably for washing wool and cot ton for weaving.  The Egyptians used a similar recipe and used soap for washing and treating skin diseases, as did the Romans.

The recipe for soap hasn’t changed much in thousands of years and soap can be made in a cold or hot process. In a cold process, room temperature lye [sodium hydroxide in water] is mixed with a vegetable or animal fat. As these ingredients react, the mixture heats up and thickens and then it’s poured in to a mould and becomes solid. It’s allowed to sit for a few weeks to cure, so the excess water evaporates. The hot process is the ancient way to make soap and the ingredients are heated up so the mixture becomes liquid. This means when it’s poured in to the moulds, it’s ready as soon as it’s solid.

People have known about how important hand washing is for a long time, even if they didn’t understand why it worked with preventing diseases. We didn’t always know about germs but many of the world’s religions promoted hand washing as part of their rituals. It was only in the 19th century that germs were discovered and hand washing became really important in medical procedures and it took longer to communicate this information to the public.

The importance of soap and hand washing has become big news with the Corona virus. Soap wipes out the Corona virus as soap dissolves the fat membrane surrounding it, causing the virus to fall apart like a house of cards. We need soap as well as water when we wash because the Corona virus is sticky to our skin through hydrogen bonds.  Soap contains amphiles which are similar to the lipids in the virus membrane and the soap molecules compete with the virus membrane lipids and break it up. As our hands are sometimes tough or have wrinkles, we need to really rub and work on washing our hands to make sure that every part of our skin is washed as much as possible.  Work up a good lather when washing hands as the friction helps to have a really good wash and it’s recommended to wash for at least 20 seconds, for as long as it takes to sing Happy Birthday twice. Don’t forget your fingernails!! Make sure to dry your hands well afterwards as well.

The Corona virus may change hand washing habits for a long period of time for the better and help reduce other things like flu. “Wash your hands like you’ve been chopping  jalapeños and you need to change your contacts,” Dr Bonnie Henry, a Canadian health official said recently. Wash early, wash often, and wash well. We are all in this together and can protect each other and those we love by being more aware of how and when we wash our hands.  Here’s our great friend immunologist Prof Luke O’Neill of TCD demonstrating the correct way to wash your hands with RTE’s Claire Byrne.

You can find up to date information on the situation in Ireland on