Basically if a baby gets something in their mouth before they get it on their skin they wont become allergic.

This starts in the womb so exposure by the mother to a variety of things is healthy even though official advise has been for mothers to avoid dirt and fermented foods.

What also needs to be limited is food stuff being used in skin care products aimed at kids. It's always the middle class kids whose parents went out and bought vegan strawberry and kiwi baby wash with natural coconut oil who have a whole range on allergies, not the poor kid who got Johnson's baby oil and sudocrem.