While shedding is normal for most breeds of dog, canine hair loss leads to bald patches on a dog's body. Known as alopecia, hair loss affects all types of dogs and develops over time or suddenly, depending on the cause. Some cases of alopecia are limited to problems with the skin itself, while other cases reflect an underlying medical problem, according to PetMD.
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Significance
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Excessive hair loss, especially in irregular patterns or combined with other symptoms such as itching and crusty lesions, signals a need for veterinary treatment. While many diseases and infections can trigger alopecia, the most common causes of dog hair loss include dermatitis, mange, ringworm, and hormonal conditions called Cushing's disease and hypothyroidism, according to Vetinfo. Left untreated, skin problems make a dog's life uncomfortable, and hormonal problems cause ongoing, systemic degeneration.
Skin Conditions
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Of the skin conditions, dermatitis, which is usually an allergic reaction to something in a dog's environment, causes skin irritation in addition to hair loss. Mange, which is caused by parasites living in the skin, produces scaling, itching and blistering, plus the hair loss. Ringworm, a fungal infection, also can produce scaling and itching, plus pustules and draining, according to Pet Education.com. These obvious symptoms will appear in the patchy areas where a dog has lost hair.
Hormonal Conditions
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Canine Cushing's disease and hypothyroidism trigger hair loss and other unusual symptoms. With Cushing's, a complicated disorder caused when the adrenal glands produce too much of the hormone cortisol, dogs will experience thinning skin along with the hair loss, plus bruising, increased thirst, malaise and an enlarged abdomen, according to Pet Education.com. With hypothyroidism, a condition in which the dog's thyroid gland does not produce enough thyroid hormone, alopecia comes with yeast infections, malaise, reduced heart rate and possibly skin pigmentation.
Diagnosis
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Diagnosing the reasons for a dog's hair loss begins with a full medical history that considers the type and severity of any skin lesions and itching, and how long the dog has been losing hair. The vet will scrape off a small amount of skin to biopsy for bacterial, fungal or parasitic infections, according to VeterinaryPartner.com, and order a blood workup and urinalysis. The vet may also order thyroid and adrenal hormone testing.
Treatment
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Treatment depends on which disease or condition has been diagnosed. Allergic dermatitis can be controlled with antihistamines, steroids and restricting contact with the allergen, according to Pet Education.com. Mange and ringworm require their own medications. Hypothyroidism is treated with daily thyroid medication, and Cushing's disease has a variety of treatments depending on its cause. Treatments should clear up infections or control conditions and allow the dog's body to regrow hair in the affected areas.
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