My husband like to sniff my used underwear, I caught him

My husband like to sniff my used underwear, I caught him yesterday doing it in the laundry room. I didn't open the subject with him, but I'm worried? We've been married for 5 years, and he look normal to me, out sexual life is great, and we have 2 adorable girls what to do? Should I shut up and don't open this subject with him? or should I ask him to see a specialist? I'm shocked by what I discovered