Asked by: Richard Somerville, Northamptonshire
The structure of soap molecules enables them to remove dirt with ease. They consist of a hydrocarbon chain, with a sodium or potassium atom at the end. The hydrocarbon end is attracted to oil and repels water, whereas the other end attracts water. When you wash your hands, oily dirt particles are surrounded by soap molecules with their water-loving heads facing outwards. This breaks up the dirt and lets it wash away in the water.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.