Hello,
Welcome to Just Answer and thanks for your question. This can be a real problem. All permanent dyes contain roughly the same active ingredients and if he is allergic to one of them, he would be allergic to all of them. He can try the temporary colors that last only 6 weeks and wash out gradually, but he may be allergic to those as well. If he is, he may have to learn to love the gray moustache.
Nurse Practitioner
Board Certified Nurse Practitioner, MS, RN. Private practice and hospitalist experience.