I am so sorry your cat is suffering with this. It sounds like Alopecia:
The hair loss in psychogenic alopecia is usually symmetrical in distribution, and typically found over the trunk, belly, the inner thighs, groin, or the rump. Sometimes cats lick themselves bald; other times stubby, broken hairs remain. Cats lick, bite, chew, or pluck at the hair. The skin may be normal or it may become red and irritated. You may notice your cat producing more hairballs, or your cat might become constipated from taking in the excess hair. Some cats may hide their excessive grooming behavior from you and are known as "closet lickers."
Stress in your cat's life can provoke excessive grooming. This usually involves a change in your cat's environment such as moving to a new home; a change in the owner's schedule; the addition or subtraction of a family member, including other animals; aggression among cats in the household; moving furniture around; seeing a new animal outside; or boredom and frustration. In addition, you may be unaware of other stressors in your cat's life. Self-grooming behavior relaxes cats, so when they become anxious, they may over-groom. Over time, the behavior becomes a habit-forming self-perpetuating cycle, and unrelated to the environmental or internal stressors. It evolves into a type of "compulsive behavior," and may progress to extreme self-mutilation and self-aggression, signs often seen in feline hyperesthesia syndrome. It is a self-reinforcing behavior, involving the release of endorphins (happy hormones).
There is no diagnostic test for psychogenic alopecia. It is diagnosed by excluding other diseases, especially diseases of the skin which may include:
Your veterinarian will perform a complete physical examination and include a variety of diagnostic tests in the workup. These tests might include:
Medications and diet trials are used to eliminate external parasites and food allergies as causes. Many times, an underlying skin disease may initially lead to the excessive grooming, which then turns into the habitual and compulsive behavior, complicating the picture. If all of the diseases are ruled out or have been properly treated, then psychogenic alopecia may be diagnosed by exclusion.
Psychogenic alopecia is treated by decreasing stress in your cat's life. This includes behavior modification, increasing playtime with your cat, and decreasing his boredom by enriching his environment with stimulating activities. Ignoring his excessive grooming behavior is important, especially if he is seeking attention with this behavior, because giving him attention will inadvertently reward the over-grooming behavior. Sometimes, engaging the cat in other behaviors such as feeding or playtime before he begins another bout of grooming might be helpful. Do not punish his behavior. This might increase his anxiety, and thus increase the over-grooming behavior.
Your veterinarian might suggest trying protective collars (Elizabethan collars), or bad tasting sprays or gels while trying to break his habit. If the problem is thought to be due to social stressors, it might help to offer him escape routes such as perches, cubbies, and hiding tents so he can escape torment by other cats in the household. Separating him from the offending cats may be very helpful. It is reported that extra attention, and play at least ten minutes twice daily can be a useful strategy in some cats.
Sometimes anti-anxiety or anti-depressant medications are necessary and will be prescribed by your veterinarian. These drugs are usually given for about twelve weeks, or until the symptoms decrease. Then they are slowly tapered. Some cats may not be able to taper off the drugs and will require them indefinitely. Your veterinarian will monitor blood tests to check for medication side effects. Many of these drugs, though widely prescribed, are not specifically approved for this syndrome in this species, so your permission is required. Your veterinarian may also refer your cat to a behavior specialist. In addition, therapies such as homeopathy may be helpful.
Please let me know how your cat is doing. I hope all will be well.
The only safe calming agent for cats is rescue remedy which you can get at any pet store.
The bad smell concerns me because it indicates infection. He must be seen ASAP for and antibiotic.A shot of Depo medrol will help as well
Please let me know how he is doing.
Sincerest best wishes,