Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry about this concern for Friski.
In most cases, cats lose hair because of overgrooming or excessive licking although many cats will engage in this behavior when you're not present to see them do it. Their hair will rarely just fall out on his own. Unfortunately, there could be several different reasons why he's losing his fur in these particular areas of his body; there wouldn't be just one specific reason. In no particular order, they are:
1. Fleas. You may or may not see fleas since they can hop off and on a cat's body and they can be ingested from all the grooming. Cats typically become allergic to the flea saliva and literally one or two fleas can drive them crazy. And, the areas of their bodies that they tend to lick a lot are often the spine in front of the tail, the stomach and sometimes the backs of the legs, too. So, I would want to rule this problem out just to be safe by use of a good topical flea product such as Advantage or Cheristin if you're not currently using such a product.
Even indoor cats can suffer from these external parasites just in case you were wondering.
2. Psychogenic which is exactly what it sounds like. These cats overgroom their bodies because of stress or change in their environment and serves as a way of soothing themselves. Some studies have shown that many cats previously thought to suffer from this condition actually have inhalant allergies (see below).
When these cats overgroom, they tend to leave "peach-fuzz" type fur on their bodies; they are not actually bald or have sores like would be seen in other skin conditions. Classic target areas are the stomach and back of the legs since they're easily accessible areas to reach.
3. Inhalant allergies to such things as dust mites, mold, grasses, trees, etc. These cats can lick just about anywhere on their bodies with this problem. They may or may not respond to antihistamines (see below) but they almost always respond to steroids which can help with the diagnosis.
4. There are other possibilities as well such as to food (but the affected areas are usually different such as the head or neck) or mites (but these cats are usually intensely itchy) so they seem less likely to be the problem.
As to over the over the counter treatment options, antihistamines can help in some cases.
Benadryl at a dose of 1/2 of a 25 mg tablet given twice daily or
Chlorpheniramine at a dose of 2-4 mg twice a day or
Claritin (Loratadine) at a dose of 2.5-5 mg/cat or
Zyrtec (cetirizine) 5 mg/ once or twice a day
It is important to ensure that the formulations used contain ONLY the antihistamine and are not combination products (e.g. Claritin-D contains pseudoephedrine, which could cause very significant adverse effects in a cat).
Sedation is a common side effect with these kinds of drugs.
I hope this helps to provide possible explanations and treatment options. Deb