Looks like chin acne. If youāre not using stainless steel bowls, switch over. And also make sure to keep clean and dry. I usually try to wipe Louieās chin/face after he eats and drinks.
That's chlorehexidine and will hopefully help soon! Be careful so he doesn't get any in his mouth or eyes! When Castor needs chlorehexidine shampoo etc I often use thin latex gloves (the kind dentists/doctors use) as I find it dries out my skin too much (although it works brilliant on Castor!). Good luck!