When faced with a cat which is suffering from itchy skin I always look for external parasites which may be causing the irritation before I do any further investigations. In the vast majority of cats suffering in this way I will find fleas are the cause of the problem. A cat with itchy or pruritic skin may spend an excessively long time grooming or scratching itself and sometimes very observant owners may notice this. In many cases the cat seems to hide this activity and the problems are only noticed when skin rashes (miliary eczema) or bald patches appear. Even then owners may still be unaware that excessive grooming is occurring.
When a cat is presented to me with bald patches or miliary eczema (named because the scabs on the skin feel like millet seeds when you run your hands along the cat's skin) I always ask if the cat is being treated for fleas. Even if the owner has never seen fleas on the cat it is still possible that they are present and causing the cat to itch due to an allergic reaction to their bites. If your cat has bald patches of skin, especially along the back or the groin and inner thighs then always consider fleas to be a potential cause. Likewise, if your cat has miliary eczema most vets will suggest a flea control regime be implemented regardless of whether you have seen fleas or not. (There is a very simple test which you can perform at home to check if fleas are present on your cat. Put a large piece of damp, white tissue paper under your cat. Comb your cat's coat thoroughly, especially the back and rump areas over the tissue paper. Search for brown specks of debris on the white paper which absorb water and produce a reddish ring around them. These specks are flea faeces and indicate the presence of fleas on your pet.) For much more information about fleas and their control see the sections on fleas and on Program.
Although fleas are the most frequent parasites to cause pruritus (itchiness) in cats there are a number of others which often cause problems. Ticks often cause localised itching and may also cause other problems since they are capable of spreading several diseases including haemobartonella and Lyme disease. Granulomatous lesions may also form where a tick has bitten a cat.
Lice are seen less commonly than fleas or ticks. The biting louse Felicola subrostratus may cause pruritus in cats. Often the whole body is affected and some areas of inflammation and hair loss may be noticed. The lice themselves are only about 1mm in length and it is often easier to spot the eggs which are attached to the base of the hair shafts. The eggs are an off white colour and look a bit like dandruff or scurf, but they are stuck to the hair and will not come away from the shaft as dandruff would.
Cheyletiella is a mite which may cause intense itching, together with dandruff and scaling skin. It seems to particularly affect the back. Otodectes cyanotis or the ear mite may also cause your cat some irritation. Surprisingly it may affect areas of the body other than the ear. Neotrombicula autumnalis or the harvest mite is another external parasite which may give your cat itchy skin.
There are many external parasites which cause cats to have problems with itchy skin. The product I generally choose to control such parasites is Frontline which comes as a spot on preparation or a pump action spray. I find it very effective if it is used according to the manufacturers instructions. There are also other products on the market which are very effective against external parasites and your own vet will be able to give you more information and direct you to a product which is suitable for your pet. If your cat has very sore patches of skin or hair loss associated with external parasites then further medication to relieve the itching and also possibly to treat secondary bacterial infections may be necessary. Your vet will be able to give you further advice.