Hi
Thanks for writing to the forum!
Generally boils are due to bacterial infections. Diabetes too can precipitate repeated skin infections. Personal hygiene too is important. However many skin conditions too imitate boils. You can see your family doctor or an internal medicine specialist for this to start with.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!
Has he been seeing his family doctor for these? Sometimes a propensity for boils can be a symptom of another issue. My husband's doctor had him tested for diabetes when he got a huge boil on his buttock. His hunch was right.