If your dog is losing hair on its legs, make an appointment with your veterinarian. It is important to get to the source of the problem, as there are many causes of hair loss and some of them can be detrimental to your dog's health.

Allergies

Allergies, such as food or seasonal allergies, can cause your dog to lose hair on its legs. Your dog may scratch, lick or chew on its skin due to the discomfort, causing hair loss and skin irritation.

Mange

Mange is a condition caused by tiny mites, and can cause itching and hair loss. The dog's front legs are a very common area for hair loss to occur.

Ringworm

Ringworm is a fungal infection that causes round, hairless patches to occur. This condition is contagious to humans, too. The legs are one of the most common places for ringworm to occur in dogs.

Hormones

Hormone imbalances can cause hair loss in dogs, and the loss is often symmetrical and not associated with itching. Hypothyroidism, estrogen imbalances or adrenal gland issues can all cause hair loss.

Staph Infection

A staph infection is a bacterial infection that causes skin lesions that can lead to hair loss. While the dog's trunk and chin are most likely to be affected, hair loss may occur anywhere on the body, including the legs.

Pressure Sores

A pressure sore is a hairless area of thickened skin. This callus is usually caused by the dog lying on hard surfaces; it may be gray in color.

Source:

Nzymes: Identifying Skin Diseases in Dogs

All About Dogs: Canine Skin Problems & Diseases