See a Doctor and have it checked as their are so many things it could be.
If his head was shaven at a Salon he could have caught something from unclean shaver etc.
If it keeps getting bigger it could be Impetigo is a contagious skin infection caused by staph or strep. A friend of mine got it in his hair after sharing a set of headphones at his job. Theses things happen so beware.
Published 22nd November 2019