It is sensible for parents to make sure their baby is always clean. Parents do their best to keep dirt away from babies. A scientist says dirt is important because it makes babies stronger. Dr Jack Gilbert did research into how dirt affects children. His research is in a book called 'Dirt is Good: The Advantage of Germs for Your Child’s Developing Immune System'. He said: "It's fine to wash their hands….but if a dog licks their face, that's not a bad thing."
Dr Gilbert said letting children get dirty was good. The dirt helps babies to build their immune system. Children often get allergies because parents clean everything that children use. This makes children's immune systems weaker, which can cause asthma and food allergies. Gilbert said the "five-second rule" is OK. This is when you eat something that fell on the floor for fewer than five seconds. Gilbert says it is OK if the floor isn't really dirty.