Sudden swelling of the face, lips, ears, and eyelids can be caused by a hivelike allergic reaction called urticaria. The cat’s head may appear strangely out of proportion to her body, and the eyes may be swollen shut. Common causes are food allergy, contact and inhalation allergy, and the bites and stings of insects. Swelling may appear as much as 20 minutes after exposure to the allergen.
Treatment: Most reactions subside in three to four hours. Cool compresses may relieve some discomfort. Your veterinarian may choose to administer adrenaline or an antihistamine. You should try to find out what caused the allergic reaction so you can prevent your cat from coming into contact with that allergen again.
Bad breath, also known as halitosis, can be caused by a variety of health problems. Don’t worry, your cat’s breath isn’t supposed to smell minty fresh-but if there’s an extremely strong, fetid odor, there could be an underlying medical problem.
The addition of wheezing, respiratory distress, vomiting, or diarrhea indicates a potentially serious allergic reaction. Snakebite is another possibility. Seek immediate veterinary attention.
Head and Neck Abscesses
Head and neck abscesses appear suddenly and are accompanied by fever. They are extremely tender and may give a lopsided look to the head, face, or neck. Opening the mouth causes extreme pain in some cases. These cats refuse to eat or drink. Many have a high fever.
WebMD Veterinary Reference from "Cat Owner's Home Veterinary Handbook"