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Hair Loss Info
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Hair Loss Blog Topics
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Dr. Michael Dym
Holistic & Conventional Veterinarian
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"Over 19 years of caring for
the well-being of pets"
Visit his Ask the Vet blog.
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Causes of Hair Loss in Dogs and Cats
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What Can Cause Pets to Lose Their Hair?
Hair loss in dogs and cats can appear as areas without hair (bald patches or alopecia) or areas with thinning hair. There may also be changes in the skin with increased pigmentation, redness, swelling, crusting, flaking, or moist oozing and discharge. There may be an unpleasant odor. If hair loss is caused by malfunction of adrenals, liver, kidneys, ovaries, testicles, or thyroid, pets may also have these signs:
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Behavior changes and irritability
Lethargy
Restlessness
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Weight gain or weight loss
Increased water consumption
Increased urination (polyuria/polydipsia or PU/PD)
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How Is the Cause of Hair Loss Diagnosed in Dogs and Cats?
Hair loss in dogs and hair loss in cats is caused by so many different medical and behavioral problems that taking a thorough history is essential to steer the diagnosis toward problems caused by illness, infection, stress, surgery, behavior, pregnancy, parasites, vaccinations, or drugs. In addition to a thorough history, some of the following medical tests can be necessary to reach a diagnosis: combing for flea dirt, skin scrapings, skin biopsy, skin culture, hair culture for fungal growth, blood test, urinalysis, X-ray, and Woods lamp illumination.
Evaluating Hair Loss in Dogs and Cats
Before ordering medical tests, veterinarians evaluate:
- The pattern of hair loss
- Whether the hairs fell out or were chewed out
- Whether there are signs of systemic illness
Patterns of Hair Loss in Dogs and Hair Loss in Cats
Among the hair loss in dogs and cats, patterns may include:
- Thin all over
- Thin over the back and sides
- Thin over the ears
- Thin along the neck
- Thin under the belly
- Complete loss along sides and down tail leaving the tip with hair (like a lion's tassel)
- Circular patches of baldness
- Bald abdomen
- Bald patches on fore legs above the wrist (carpus)
- Bald patches on back legs on the side above the ankle (tarsus)
- Balding along the back of the hind limbs up over the scrotum
Generally, the pattern of balding or thinning suggests the cause of hair loss. For example, pets with chewed off hair and bald, patchy areas over the base of the tail, inside the back legs, and on the abdomen often have fleas. Pets with thin skin and hair loss along the back and sides, and down the tail, but not the tip of the tail often have high cortisol levels and Cushing's disease. Pets with thick skin, weight gain and dull, thinning hair over the back and sides often have low thyroid levels and hypothyroid disease.
Hair Loss Due to Chewing and Shedding
To evaluate whether hair was chewed off or fell out, hair is put under the microscope. Hair that falls out has a root with a little bulb. Hair that is chewed out does not end in a smooth bulb. Hair that falls out suggests illness, hormonal, or endocrine problems, but hair that is chewed suggests fleas, other external parasites, or behavioral problems.
Signs of an Underlying Disease or Illness
Often pets that are ill hide symptoms and we first realize they might be ill because the hair falls out. For example, pets with Cushing's disease begin drinking more and urinating more, but we might not notice until we realize their hair is falling out on their sides. Pets with hypothyroid disease become lethargic and put on weight, but we might not realize this is a medical problem until their hair thins or fails to grow back in after they are clipped.
Medical Tests for Diagnosing the Cause of Hair Loss in Dogs and Cats
The following are tests done to diagnose the cause of hair loss:
Test |
Used To Identify |
What Test Confirms |
Combing for flea dirt |
Fleas |
An especially important test for pets that groom themselves and remove fleas efficiently—especially cats. By finding flea dirt, we confirm that fleas are a problem for the pet. |
Microscopic exam of skin scrapings |
Demodex mites
Lice
Scabies
Yeast |
Some parasites living on the skin or in tunnels in the skin are extremely difficult to find. If the parasite is found, this is a positive test. If no parasites are found, it is possible they are still causing the problem but have eluded us.
Yeast organisms are easily identified on skin scrapings and can explain why a pet is itchy if there are no lice, mites, or fleas. |
Microscopic exam of ear discharge |
Ear mites |
In some cats thinning of hair around the ears on the face is due to mites |
Culture of skin discharge |
Bacteria |
Culture and sensitivity tests find the cause and the best treatment for the infection so that money is not spent on ineffective medications. |
Fungal culture of hair shafts |
Ringworm
(Dermatophytosis) |
Some pets—usually cats—carry ringworm that doesn’t bother them but does infect other pets. Culturing all pets in the house helps identify pets that are obviously infected and those that are silent carriers of ringworm. |
Skin biopsy |
Pemphigus,
Squamous cell carcinoma
Basal cell carcinoma
Mast cell tumors
Melanoma
Vaccine-induced Dermatopathy |
Immune diseases, skin cancers, and vaccine-induced skin diseases are confirmed by biopsy specimens. |
Blood tests |
Diabetes
Cushing’s disease
Hypothyroidism
Hyperthyroidism
Sex hormone alopecia
Lymphoma |
Pets with endocrine diseases and those with cancer of the blood, such as lymphoma, are diagnosed with blood tests. |
Urinalysis |
Diabetes
Cushing’s disease |
Urinalysis helps diagnose the severity of diseases. For example, when diabetes is severe there will be sugar and ketones in the urine. Urinalysis helps diagnose Cushing’s disease by comparing the ratio of cortisol to creatinine. |
Woods lamp illumination |
Ringworm (Dermatophytes) |
Some ringworm organisms fluoresce under a Woods lamp, but some do not. Pets with a negative test may still have ringworm infections. |
X-ray |
Cancer |
Internal cancers that can cause rapid hair loss with hair that pulls out in clumps may be diagnosed with X-rays. |
Weight |
Cancer
Diabetes
Hyperthyroidism |
Rapid weight loss indicates hair loss is caused by a serious organ disease. |
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