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Determine whether the cat has been fighting. Assess whether an ear lump is a haematoma. Have cysts removed. Consider a potential food allergy. Rule out flea bites.

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Abscesses are a common type of lump that usually form a few days after a fight with another cat or dog. They are rather large and filled with fluid. If you notice your cat seems feverish or unwell and has a lump with a scab in the middle, it is likely an abscess. Abscesses are bacterial infections. While they are usually not too dangerous, it’s best to have a vet look at them. They can drain the fluid and prescribe your cat antibiotics to rid their body of infection. Blood can collect beneath the skin at the site of a minor injury. This will form a swollen, fluid-filled lump called a haematoma. Haematomas are common on cats that shake their head vigorously and damage the capillaries between the cartilage and skin of their ear. Haematomas need to be evaluated by a veterinarian. There is usually an underlying cause of a haematoma, which requires treatment. For example, it may be the result of ear mites or an infection that caused your cat to damage their ear. Some cysts may be caused by blocked hair follicles or oil ducts. If a lump appears suddenly but doesn’t change, and has a hair growing from its center, it may be a cyst. They can be left alone if they do not repeatedly get infected or bother your cat. If you're unsure, the safest option is having a vet check on a cyst and determine whether it should be removed. If you have recently changed the type of food you feed your cat and notice lumps on their head and neck, the lumps are likely evidence of an allergic reaction.  Discontinue feeding them that food and see if the lumps subside.  Lumps of this sort will be small, pale, and filled with fluid. While the lumps themselves are not dangerous, your cat may hurt itself by scratching. If lumps are small, reddish, and slightly pointed, they are likely flea bites.  They will usually be accompanied by scratching, and maybe hair loss.  Talk to your vet about how to get rid of the fleas, and watch out for wounds on your cat’s skin where they are constantly licking and scratching.