Dermatology cases account for more than 80% of veterinary visits worldwide and are the most common health problem reported by dog owners and veterinarians. Skin is the largest organ of a dog’s body and is its first layer of protection against external pathogens and physical damage. Its continuous exposure to various elements makes it highly susceptible to inflammation, infections, and injuries.

Anatomy and Function of the Skin and Hair

The skin is composed mainly of 2 layers: the outer epidermis and the inner dermis layer. The epidermis protects the deeper layers of the skin from foreign materials and the external environment while the dermis provides support and nourishment to different skin appendages like the hair strand, the follicle, and the glands that are associated with it.

Dogs have compound hair follicles comprised of 3 central hairs and approximately 15 smaller secondary hairs all exiting from one pore. The hair coat adds another layer of protection to the skin and helps regulate body temperature. Sebaceous glands attached to the hair follicles produce an oily substance called sebum that helps keep the skin moist and soft.

Damage to the hair follicle and the structures around it triggers an inflammatory response which disrupts the normal physiology of the skin layers and the structures housed in it. This often leads to clinical signs such as skin dryness, itchiness, and loss of hair.

Common Causes of Alopecia in Dogs

As mentioned, alopecia is mostly a clinical sign secondary to an underlying condition. When a dog is presented with hair loss, the main goal in managing it is by determining the underlying cause and giving appropriate treatment. Once the underlying condition is addressed, hair loss should also be controlled, and hair grows back over time. Some of the common causes of alopecia in dogs are:

1. External Parasites and Superficial Infections

Primary causes of hair loss include external parasite infestation and infections. Most external parasites are contagious, and an infested dog can easily transfer the parasite to other individuals. The presence of ticks, fleas, and lice can cause inflammation and subsequent hair loss in dogs. Sarcoptic mites invade and live under the superficial layer of the skin causing alopecia in dogs and cats. Demodectic mange is one of the most common causes of hair loss in younger dogs.

Superficial infection with bacteria and fungal spores infiltrates hair follicles and hair roots causing an inflammatory response and alopecia. These infestations and infections often cause severe itching which worsens hair loss.

2. Allergies

Whenever a dog shows signs of hair loss, the first thing that comes into the mind of most people is allergies. Allergic dermatitis is arguably the most common cause of alopecia in dogs. Allergic reactions, however, are not that simple. They can take many forms and have different causes, which require rigorous diagnostic steps to pinpoint.

Flea bite allergy dermatitis is a documented allergic reaction of dogs to the saliva of fleas. This causes severe pruritus and hair loss, often in the rump region of the dog’s body. In most cases, even after the flea infestation has been controlled, signs of dermatitis persist and will need appropriate treatment.

Food allergy is considered a common cause of allergic dermatitis in dogs. Food allergy dermatitis happens when an ingredient in the food, oftentimes the protein component, is recognized by the dog’s body and an immune reaction is mounted against it. Most food allergy cases cause dermatology signs like severe scratching, skin redness, and eventual alopecia. Secondary skin infections are quite common in dogs with food allergy dermatitis.

Atopic dermatitis is a condition in dogs where they develop an allergic reaction to practically everything from the environment like pollen, dust, and grass. Dogs diagnosed with atopic dermatitis will require life-long treatment to manage the clinical signs.

3. Hormonal Imbalance

Several hormonal imbalances in dogs have hair loss as a clinical sign. Hormonally-induced conditions are often explored if infectious and allergic causes of hair loss have already been ruled out. However, it’s important to note that hair loss alone is not enough to consider hormonal imbalance in dogs, and other symptoms have to be present as well.

Hypothyroidism is one of the most common hormonal causes of alopecia in dogs. Thyroid hormone plays an important role in a dog’s metabolism and normal physiological function. A decrease in thyroid hormone production slows down the body’s metabolism causing a rapid increase in the dog’s weight. The condition also affects normal hair growth and causes bilateral (symmetrical) alopecia, often with no apparent skin infection or inflammation.

Abnormalities in the cortisol production of the body also cause hair loss in dogs, among other symptoms. Hypoadrenocorticism, or Addison’s disease, is the insufficient production of cortisol hormone caused by problems in the adrenal gland, pituitary gland, or hypothalamus. Hyperadrenocorticism, or Cushing’s disease, is the abnormal increase in the production of cortisol caused by tumors located in the adrenal glands or other glands that influence its activity.

Since cortisol affects practically all types of cells in the body, changes in the levels of the hormone cause a multitude of clinical signs affecting different systems of the dog’s body. Both conditions cause loss of hair without signs of inflammation on the skin. Clinical signs, particularly alopecia, can be managed with specific treatment to normalize cortisol levels in the dog’s body.

A breed-specific condition called Alopecia-X causes severe, generalized hair loss in Pomeranians and similar breeds. This occurs as a result of an imbalance in the sex hormones (testosterone, estrogen) and is often accompanied by an abnormally low melatonin level. Hair loss is often generalized and aggressive and the skin usually becomes dark due to excessive pigment production.

Dogs diagnosed with Alopecia X would need to be neutered or spayed to control sex hormone imbalance. Melatonin supplementation helps speed the regrowth of hair and control the excessive pigment production of the skin.

Read more:

Ditch the Itch: Skin Allergies in Dogs

My Dog Won't Stop Licking His Paws - Help!

Ringworm in Cats and Dogs

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