Majority of men end up with reactions, especially on their chest. I think because he is in contact with you as you are his Mom, you know about it. Plenty of men have done the wax once and not ever again because of this.
It's important to prepare a client and let them know this can happen. I suggest to all my male chest waxes to take an antihistamine the day of their waxing. I thoroughly cleanse their skin and apply soothing post wax lotion at the end. It's a good idea to take an additional antihistamine the following day.
As long as the client knows, they don't freak out and every one has become a loyal client.
P.s. I get the same itchy, hives reaction on the inside of my elbows and wrists when I wax my arms.