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Dogs, like humans, have a tendency to have growth pattern changes in their hair. For some, it’s as normal as seasonal or allergenic responses to the environment. However, for others, it’s a sign of a more complex problem such as a hormone imbalance or a disease.

Seasonal ChangesIn the winter, hair growth increases to help keep the dog warm.

    • The most common reason that a dog might have a change in hair growth is a simple change in season. When the atmosphere becomes warmer, a dog must thin its coat by shedding and slowing its hair growth in order to keep cool in the hot summer heat. In contrast, when it gets cooler outside, a dog must conserve heat by growing its hair faster to keep warm.

      Allergic Reactions

    • Allergies are another common reason a dog may have a pattern change in its hair growth. As with humans, dogs may get the runny nose and watery eye symptoms of allergies, but they may also begin to have thinning hair in their coats. Dogs have many allergies that are similar to those of humans, such as air-borne allergies from pollen and allergies to types of molds and foods. Fleas can also cause a type of allergy in dogs. This kind of irritation can cause the dog to lick, chew and scratch obsessively, which can eventually lead to a thinning coat and usually pertains to only the parts of the body affected by the licking, chewing and scratching.

      Hormone Imbalances

    • When a dog has hormone imbalance, its hair growth can be affected. Common imbalances involving androgen, progesterone and estrogen cause the resting cycle of hair follicles to be lengthened, causing an apparent change in hair growth, according to Dogs that have been diagnosed with diabetes, and even ones that haven’t, can have a problem with insulin levels, which can affect hair growth. Another common imbalance causing a dog’s hair to cease growing is when there is an abnormally low quantity of thyroid hormones being produced.

      Diseases and Conditions

    • Hair loss, also known as alopecia, is a common sign associated with many diseases and conditions. Malnutrition will commonly cause hair follicles to slow in the growth process. It takes an immense amount of nutrition and protein for new hair to replace old hair. If the nutrients are lacking, a dog’s hair can become brittle and hair growth can be slowed. Solar dermatosis, a skin reaction to sunlight, can cause a dog’s coat to thin, according to Hair loss can also be a symptom of ringworm, lice and even pregnancy.


    • Seasonal hair growth and thinning is natural and is not a threat to a dog’s health. Treatments for allergies can be as simple as changing the dog’s medication, seasonally treating for fleas or pollen, or even just changing the diet, such as changing dog food brands. However, more complex allergies, as with hormone imbalance treatments, can result as a life-long need to have medication every day. Although growth pattern changes in dog hair can typically be easy to treat, they can also be signs of a larger problem and may require a veterinarian’s attention.