I have no idea if this will help but I have almost the exact opposite problem. My son learned somewhere about over washing of hands, sanitizers, etc. making immune systems weaker because there isn't as much exposure for which immunities can be developed. He also learned somewhere that picking his nose and eating what he finds boosts his immunity. He thinks of germ exposure as a challenge his immune system needs to meet head on. Anyway, I wonder if you could find some of that information and share it with your son. Maybe it would take the edge off the germ fear.
