Hair loss, or alopecia, in a dog or a cat is not an uncommon problem for veterinarians to see.

The causes of this are many and varied. Parasites such as fleas and mites are frequent causes. Hypothyroidism, which is an underactive thyroid gland, and Cushings disease, an overactive adrenal gland, are common hormonal causes.

The frequently vexing and complicated field of dermatology is one of the reasons that I (Dr. Henri Bianucci) became a surgeon. Now, my primary involvement with skin is cutting through it, not treating and diagnosing skin conditions. But I do have an appreciation for the art of dermatology, and a recent case caught my attention.

My friend and colleague, Dr. Randall Thomas of Southeast Veterinary Dermatology and Ear Clinic in Mount Pleasant described a small-breed dog who had a severe case of alopecia.

Because there was no skin irritation or itchiness and the fact that it was symmetrical (the same pattern on both sides of the patient) and diffuse, his primary suspicion was that this was a problem born of a hormonal imbalance.

Next, a biopsy was taken of the skin, which confirmed that this was likely a hormonal problem. Initial blood work, however, was negative for all of the usual hormonal imbalance suspects.

Thomas scheduled more testing for some of the less common hormonal issues. It was then that the owner, a woman he gauged to be in her mid- to late-40s confided in him and asked a question.

“I am on hormone replacements. Do you think this could be the problem?” He was surprised by the question, because he had never diagnosed a case of that before.

But it started to make sense. The dog was one of three in the home and was the smallest so it was frequently picked up and handled. This would mean that exposure to the owner would be proportionally greater for him than for the larger pets. Although mildly so, there was some evidence of hair loss in the other dogs.

The woman was administering her hormones through a transdermal gel. The mix of estrogen, progesterone and testosterone was rubbed on the inside of the forearms where it is rapidly absorbed through the relatively thin skin. This also is applied as a spritz or spray as well.

The decision was made to apply the gel elsewhere, such as the back, and to wear gloves or thoroughly wash hands after application. These simple alterations in application resolved the problem, and full coats of hair returned to all three dogs.

Hormone replacement therapy is a rapidly growing field worth $1.8 billion in 2009. Topically applied gels make up a large and expanding part of that market. Use with care around pets and children.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to