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.
Sneezing, congestion, watery eyes and nose....Has your cat caught a cold? It could be feline herpes, also known as feline viral rhinopneumonitis (FVR), rhinotracheitis virus and feline herpesvirus type 1 (FHV-1), and one of the most common causes of upper respiratory infections in cats. Many cats are exposed to this virus at some point in their lives.
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"