Of course, there are other causes of cats hair loss. Cats can have a type of obsessive/compulsive disorder and lick themselves until their skin is raw. Sedatives and antidepressants along with Feliway can help such disorders, but there is no doubt in my mind that this is not the problem that Whiskers has. Also, the open sore on his lip is almost definitely not from his licking, but is another allergic reaction to the fleas, often referred to as Rodent Ulcer (eosinophilic ulcer). The steroids will help with that condition also.
Long-term use has the risk of creating more permanent and severe damage. Some high dose, long-term side effects include increased incidence of infections, poor hair coat and skin, immunosuppression , diabetes mellitus , adrenal suppression, and liver problems. The potential problems can be severe, however, it must be stressed that these side effects are dose dependent. Despite the potential side effects, steroids can be used effectively and safely, if a careful dosage schedule is followed. Still, because of the availability of safer yet effective therapies, steroid use is reserved until all other treatment options have been exhausted. Several studies have shown that if fatty acids and antihistamines are used concurrently with steroids that the amount of steroids needed to offer relief is greatly reduced.