Cat smell usually isn't noticeable. If your cat does seem to have acquired a foul odor, it's a sign that something is amiss with his health. Here are some different interpretations of bad feline smell.
Obvious Causes
A bad cat smell may be due to your cat having come into contact with something foul, such as feces, urine, a dead animal or a skunk. While cats are less likely than dogs to revel in bad-smelling things, there's no reason why your cat can't get a bit dirty sometimes.
Halitosis/Bad Breath
Halitosis is the most common cause of bad cat smell. Halitosis could be the result of dental decay, oral cancer or even kidney disease.
Systemic Illness
Your cat's bad smell could be the result of systemic illness, especially if accompanied by feline symptoms such as sneezing. Systemic illness often causes severe halitosis. Your vet will need to examine your cat to determine if he is suffering from a systemic illness.
Skin Problems
Skin diseases usually present visible symptoms such as hair loss, itchiness, and even sores and pustules. Cats with skin disorders may smell very bad, especially because concurrent bacterial and yeast infections of the skin are common to many skin diseases.