Section: Overview
The patterns of hair growth vary with species and anatomic location on the body. For some animals, seasonal alterations are noted. In dogs and cats, a mosaic exists and coordinated shedding cycles occur.
In some breeds the active or growing part of the hair cycle is prolonged, as in Yorkshire terriers, like it is in people. These breeds are more sensitive to drug therapy, like chemotherapy, that interfere with the hair cycle, and they develop alopecia as an adverse effect.
Numerous factors affect hair growth. They include:
Hormones. Some will stimulate hair growth while others will delay it.
Androgens. They cause courser hair with lengthened resting phase of hair follicles.
Progesterone. This produces courser hair with lengthened resting phase of hair follicles and decreased growth rate.
Estrogen. This results in fine sparse hairs and lengthened resting phase of hair follicles.
Thyroxine initiates hair growth and increases rate of new growth. A deficiency in thyroid hormone (hypothyroidism) usually results in poor hair growth and thinning of the hair coat.
Corticosteroids retard hair growth by inhibiting new hair growth, thus alopecia or thinning of hair occurs as a consequence of this type of therapy.
Growth hormone. Its lack results in retention of juvenile coat or alopecia in the adult.
Insulin. This hormone is responsible for normal growth, although diabetics may have alopecia.
Nutrition
Protein. Cystine and methionine are requirements for hair growth. Protein-calorie malnutrition is characterized by dry, brittle and sparse hairs.
B vitamins, especially pantothenic acid, (for Cu utilization) are important for proper hair growth.
Copper is important for hair production and a deficiency will result in poor hair coat.
Some breeds, like the Chow-Chow, may have an arrest in the hair growth after clipping. This resolves spontaneously after several months of lack of hair re-growth.
Excessive numbers of bacteria in the hair follicle (bacterial pyoderma) may cause circular areas of alopecia or generalized excessive shedding. These signs resolve with a few weeks (3 to 4 weeks) of systemic antibiotics. This presentation is very common in cats with allergies.
Ringworm (dermatophytosis) can also cause the hair to fall out in spots. Ringworm can be diagnosed or ruled out by submitting hair samples for fungal culture.
Mange (demodicosis) can also cause patchy hair loss. This type of mange is non-contagious and can be diagnosed by performing skin scrapings.
Veterinary Care
If your cat has been clipped and the hair is failing to grow back, it may be due to a hormonal deficiency or imbalance. In order to diagnose this, blood samples are necessary to measure concentrations of various hormones.
If your cat is losing hair in spots then it may have a bacterial infection or ringworm or demodicosis. Your veterinarian may need to do skin scrapings or pluck hairs for cultures.
Home Care
Make sure your cat is receiving a balanced diet with an appropriate level of proteins, minerals and vitamins.
Depending on the presence and the type of skin infection, you may have to use medicated shampoos on your pet or administer oral medications to clear the infection.
If you have an allergic cat, work with your veterinarian to manage the allergies without the use of steroids (e.g., prednisone) because these medications have serious systemic adverse effects and may also delay hair growth.
If your cat is diagnosed with a hormonal deficiency you may have to supplement your pet with hormones. This treatment is usually life-long.
Follow-up Care
Prevention and follow-up depends on the cause for the lack of hair growth. As a general rule, the use of steroids should be limited or avoided as they cause medical problems and arrest hair growth.
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