You must have heard “doggy smell” often, but have you ever heard something like “cat smell”? May be not, because felines keep themselves extremely clean by grooming and it is an unusual thing if your kitty is having a foul smell. Thus it is recommended to consult a veterinarian if foul odor remains for more than two days as it is believed by the vets that bad smell may be the result of underlying health issues. This bad stench depends on the part of the body that has wellness issues. Therefore the first thing you should do is to check from which body part the smell is spread and act accordingly.
These are some of the reason why your all-clean kitty may sometimes smell bad. As it is an unusual thing in case of cats, one should take it seriously and consult a vet if the condition persists for more than two days.