Hello fiestycat,
Thanks for the question.
The most common causes of hair loss in cats would be allergies or a skin infection. Each could be caused by multiple things.
Allergies-cats get miliary dermatitis which is small bumps with scabs-allergies can come from fleas, contact, inhalant, food etc.
Skin infections can come from bacteria, fungus(ringworm), skin parasites
You should have your cat checked out and several things performed.
Skin scrapings-for parasites
Woods Lamp evaluation for fungus
Consider flea preventative.
Hope that helps.
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Dr. GF
Cat Veterinarian
Compassionate, caring and practical. 20 yrs of private practice experience.