Hot spots (flea allergy dermatitis) is a skin disease (dermatitis) caused by your pet’s allergic reaction to fleas. Derm means skin, and “itis” means inflammation, so your pet will have itchy, inflamed skin. Inflamed skin is hot, red, and itchy. Often the skin becomes smelly because yeast and bacteria grow well on unhealthy, inflamed skin. When your pet scratches the bacteria are rubbed deep into the skin and hot spots develop. Hot spots are just infected sores. Pets with flea allergy dermatitis are so sensitive they can develop hot spots if bitten just twice a month by fleas. Your pet is having an allergic reaction to flea saliva, feces and exoskeleton.