There is special baby detergent that is recommended to use even after the first wash. Some moms don't bother but I have always had really sensitive skin so even at seven months old I still use dreft detergent for my son. If I don't he gets rashes
i am just because people have touched them and they're sometimes sprayed with chemicals to keep them from wrinkling during shipment from factory to store and it's just more sanitary. I do it to my new clothes too before I wear them. and if they're used I definitely do just in case the people who owned them before used a type of detergent that could aggravate the skin.