When pet scratch insect bite, the area to be wet with serum and leads eventually to painful hot spots. 4 Fleas the presence of fleas on skin can make your cat be extremely irritable. The flea has the ability to cause dermatitis and itching intense. The skin between the toes of the foot are the most affected areas. Hair loss really occurs in such cases when the presence of fleas takes to fungi or bacterial infection. 5 Scabies another skin disease that can cause excessive hair loss is scabies. It is a persistent condition which is also contagious. Deptopica Scabies is genetic in nature and Sarcoptica Scabies is contagious and causes intense itching.