How can I tell my bf he needs to clean extra good down there...

So my bf is clean and showers every day but for some reason his head always smells. It turns me off everytime I try to go down on him. How can I bring up something like that to talk about? He's sensitive about personal problems like that and I really really don't wanna imply he has bad hygiene or anything coz I know he doesn't but I don't understand what is the problem. Esp coz one time while we showered together I made sure to wash him pretty well but it didn't even last 2-3 hours. Is it a precum issue maybe or when he pees?