Citronella, perfumes, solid air fresheners and citrus are all smells cats hate. Others include aloe, eucalyptus oil, oil of wintergreen, cigarettes and carpet fresheners. Cats also dislike the smells of cleaning agents and disinfectants, potpourri, hair spray and air fresheners. A cat’s sense of smell is about 14 times more sensitive than that of a human.
A cat's sensitivity to smell may explain its fear or aversion to certain items or areas in the house. Some of the most commonly used household disinfectants and deodorizers contain phenols, which are toxic to cats. A cat's liver doesn't have enough detoxifying enzymes to process phenols, so cat owners should avoid any product containing this chemical. Cats constantly groom themselves with their tongues, so any compound they touch is likely to enter their bloodstream through the mouth. Veterinarians can provide a comprehensive list of toxic compounds on request.
Even nontoxic smells that people find pleasurable, such as natural citrus, can cause nausea in cats. Cat owners can use this aversion to protect a piece of furniture by placing fresh lemon juice, cinnamon or black pepper near it. The smells these ingredients produce help to prevent cats from scratching or urinating on household objects.