Alopecia in Dogs & Cats – Why Your Pet is Losing Hair

Growing up and through college, I had long curly Greek blond
locks of hair whenever I let my hair grow. Yet as my maternal grandfather had
male pattern baldness, I knew I wouldn’t have my hair forever. Indeed, in
veterinary school my receding hairline became obvious. Hair loss or alopecia had
set in. I had male pattern hair loss. Dogs and cats develop alopecia too.
Indeed, alopecia is one of the most common reasons pet parents bring their fur
babies to the hospital for evaluation by a veterinarian. So, this week’s post
is dedicated to alopecia in dogs and cats to raise awareness of this medical
problem. Happy reading!


Alopecia – What is it?

Alopecia is simply defined as hair loss. There are myriad
causes of hair loss in dogs and cats. Before we delve into them, let’s first
explain some basics of hair anatomy growth. Hair is composed of the follicle
and the shaft. The former is the segment found in the skin and has several
structures including the papilla (contains small blood vessels called
capillaries), the bulb (that divides frequently), and two sheaths that protect
the shaft. Follicles are intimately related to different types of glands (i.e.:
sebaceous glands, apocrine glands) and muscles (i.e.: erector pili). Hair
shafts are made of keratin, a dead protein.

Illustration of normal anatomy of skin and hair. Illustration courtesy of the Merck Veterinary Manual.

Hair grows in different phases. The phase of active hair
growth is called anagen. Hair subsequently enters a transient phase called
catagen before entering the resting phase called telogen. Once a hair enters
the telogen phase, a new hair enters the anagen phase and the telogen phase is
shed. Shedding is called the exogen phase. Hairs of different breeds of dogs
spend variable amounts in each phase. Most dogs have a telogen-predominant
cycle of hair growth. This means their anagen phase is short (1 month to a year
or more) and then hairs enter the telogen phase for a prolonged period of time,
potentially years for Nordic breeds. At some point, the telogen hair falls out
and is replaced by a newly developing anagen hair. The trigger for a telogen
hair to fall out and for a new anagen hair to grow is unknown. Some breeds like
poodles have an anagen-predominant cycle (similar to people), necessitating
regular haircuts.  

The different phases of hair growth. Illustration courtesy of the University of Tennessee’s College of Veterinary Medicine.

Alopecia – What causes it?

As I mentioned earlier, there are a plethora of causes of
alopecia in dogs and cats. Veterinarians initially categorize alopecia based on
whether or not the patient has pruritus, otherwise known as itchiness. Major
causes of itchy alopecia are allergies, infections (parasites, bacterial yeast),
and some cancers.

If patients have alopecia without itchiness, then the
alopecia is categorized based on whether or not inflammation is present. After
consideration of the presence of inflammation, veterinarians will evaluate the pattern
of hair loss can since it can provide clues about the underlying cause.

Alopecia – How is it diagnosed?

Identifying alopecia is straightforward. A pet has an area
of hair loss. The challenge is figuring out what caused the alopecia.
Veterinarians will ask a lot of questions about a pet’s environment, diet, and
previous and current medical problems. The importance of a thorough physical examination
can’t be underscored. Important findings – the feel of hair, the pattern of hair
loss, the presence of oily secretions or dandruff – can all provide clues about
the underlying cause of alopecia.

Photo courtesy of Dr. Linda Frank and the University of Tennessee’s College of Veterinary Medicine.

Understandably, some diagnostic testing is required to
determine a definitive diagnosis. Tests may include:

  • Skin scraping – to look for certain infectious agents
  • Skin cytology – to look for abnormal cells and potential infectious agents
  • Fungal culture
  • Blood & urine tests to screen for hormone disorders (i.e.: Cushing’s disease, hypothyroidism)
  • Skin biopsy

Pet parents may find it helpful to partner with board-certified
veterinary dermatologist to develop a logical diagnostic plan.

Alopecia – How is it treated?

The good news is alopecia is rarely a life-threatening
problem. But it could be a sign of a significant underlying disease that
carries a poor prognosis, especially if not identified and treated
appropriately. Definitive treatment for alopecia is based on the underlying
cause of it. Bacterial infections are treated with antibiotics. Fungal
infections are treated with anti-fungal medications. Hormone disorders like
Cushing’s disease and hypothyroidism can be managed, but parents often find it
beneficial to partner with a board-certified veterinary internal medicine
specialist to manage these diseases long-term.

The take-away message about alopecia in dogs & cats…

Alopecia or hair loss in our pets is a common problem. There
are many potential causes, and a thorough diagnostic investigation is essential
for making an accurate diagnosis and treating a patient appropriately.

To find a board-certified veterinary dermatologist, please visit the American College of Veterinary Dermatology.

To find a board-certified veterinary internal medicine specialist, please visit the American College of Veterinary Internal Medicine.

Wishing you wet-nosed kisses,