My 2 year old son was on plane days nails and dexamethasone what would cause him to pick at his face as if he was irritated and cause scabs on his fac?

Dermatitis: Your son was on what? Please consider rewriting your question a little more clearly. As far as why he would pick and scratch at the skin on his face - a local irritation causing inflammation. It could be caused from anything from excessive dryness to sunburn to insect bites or exposures to allergens.For a thorough answer it's best to have the doc look at his skin.