He has the beginning stages of Periodontal disease. he will need to go to dentist and they will have to clean the insides of his gums, and as soon as they are done, the smell is gone.. I had it..
Hi, it sounds like your cousin has some sought of gum disease, (periodontal disease) i had the same thing and one of the first symptoms was BAD breath. I found out that i had it when i went to the dentist to fill in a cavity. I hope i helped. Good luck =)