What you are describing sounds like Miliary Dermatitis.
This is an allergic skin condition in which the hair loss is typically in the tail head area, and the back legs. The skin is very itchy and the cat chews, licks, and scratches. Kitty may also "ripple" the skin often. The skin has many small scabs and bumps - supposedly they look like millet seed which is where the name comes from.
Here are some links to further information about this condition:
Miliary Dermatitis is caused by an underlying allergic condition.
The most common allergy is a flea bite hypersensitivity (flea allergy dermatitis, FAD). All it takes is ONE flea bite to cause this problem. It's kind of the same as how some people are allergic to bee stings. For most of us, a bee sting hurts a bit but isn't really a big deal. For others, however, a single bee sting can make their whole arm swell up or even cause an anaphylactic reaction that can be life -threatening.
In the same way, animals who have FAD get insanely itchy over a single flea bite.
In your situation, there may have been flea eggs brought into your home on shoes or clothes. Flea eggs are very resistant to cleaning products and can survive on the carpet for months! So, even though you may not see any fleas on your cat if a single flea hops on, takes a bite and then hops off, this cat could be insanely itchy for weeks!
So, she may have had one flea bite 8 weeks ago, and now just had a second flea bite that triggered this again. All it would take would be ONE flea to bite her to make her this itchy if she is allergic to them. This is very common in cats.
Here is more about flea control:
For more information about flea allergy dermatitis, you can check out these links:
Since this may be what has triggered your itchy cat's Miliary Dermatitis, it would be prudent to treat her with Advantage or Frontline. In Canada, you can only get these products through a veterinarian, but in the USA you can get them at large pet supply stores (Pet'SMart, etc), or even on-line.
Here is a link that may help you to find some:
Miliary dermatitis is generally treated with corticosteroids, or in a mild case with antihistamines and essential fatty acids.
You could start this cat on essential fatty acids as they are helpful at decreasing inflammation and improving skin health.
Here's a link to one example:
Antihistamines are much less helpful in cats than they are in humans and will significantly help only 25 to 30 percent of cases. Nevertheless, they are often prescribed since they are relatively safe drugs when compared to corticosteroids.
Some cats respond better to one antihistamine than another, so veterinarians usually try two or three different types before giving up on them.
I usually start with chlorpheniramine in cats.
Here is more about it:
So, in summary, what you are describing sounds like Miliary Dermatitis. This is an allergic skin condition. Often it is due to an underlying sensitivity to a flea bite. However, there may be another cause of the allergic dermatitis.
Your veterinarian would need to examine this cat in order to be able to prescribe corticosteroids but if you wanted to try something else before seeing the vet, you could treat her with Advantage or Frontline and start her on Derm Caps, and could even consider antihistamines (dose in link above).
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.