I think they mean constant hand washing. Obviously we have to wash our hands, but when you take that to an OCD place, it's not healthy. We do still need to expose ourselves to some germs in order to allow our bodies to create tolerance to them, it helps our general immunity. If you never let any germs in, then eventually when one does break through, your body doesn't have practice fighting it off, and you get sicker than you would have otherwise. It's not unlike children who are sheltered from anything and everything that might upset them their whole childhood - then when they grow up and realize nobody will shelter them from the world, they don't know how to process stress properly.