Cushing's disease, allergies and genetics can cause bald spots in dogs, according to WebMD. Fungal or bacterial infections can lead to baldness. Pressure sores develop where a dog comes into regular contact with hard surfaces, such as on his elbows or other bony areas. Typically, the skin thickens and forms hard calluses, and the hair falls out.
Dogs suffering from hyperadrenocorticism, or Cushing's disease, tend to have an overabundance of cortisol, explains WebMD. Cushing's disease typically occurs in dogs over 6 years old and includes symptoms such as frequent eating, drinking and urinating as well as development of a pot belly. A tumor on one of the adrenal glands can cause the condition; however, this is less common. Medications are effective for treating Cushing's disease, and surgery is rarely necessary for treatment.
Allergies to foods, pollen and parasites can lead to hair loss in dogs, notes WebMD. Most canine allergies are due to flea bites, and itching, biting and redness are accompanying signs. Treatments include oral and topical medications, immunotherapy, avoiding the allergen and changing the dog's diet.
Dogs that have symptoms such as oily skin, inflammation, hair loss around the eyes and mouth, thickened skin and itching may have mites, states WebMD. Additionally, ringworm is a contagious infection that causes irregular hair loss and infection. Antifungal shampoos, creams and medications treat the condition.