What Causes Hair Loss in Dogs: 5 Common Types of Causes

Hair loss in dogs, or canine alopecia, is a common concern that goes beyond normal shedding and can be caused by various factors affecting your pet’s health. While some seasonal coat changes are perfectly normal, abnormal hair loss can be a sign of underlying health issues that require attention. Understanding the difference between natural shedding and problematic hair loss is essential for maintaining your dog’s overall well-being.

From parasitic infections to allergic reactions involving dust mites and from hormonal imbalances to issues with hair follicles, the causes of hair loss in dogs are diverse and sometimes complex. Recognizing these causes early allows for proper diagnosis and dermatological treatment, helping your furry companion maintain a healthy, lustrous coat.

Understanding Normal Shedding vs. Problematic Hair Loss in Dogs

Seasonal shedding is a natural process that most dogs experience as part of their hair growth cycle. During spring and fall, dogs typically shed their coats in response to changing daylight hours and temperatures, preparing for the upcoming season. This process is more pronounced in double-coated breeds like German Shepherds, Huskies, and Golden Retrievers, who may “blow their coat” dramatically during these transition periods. The intensity and timing of seasonal shedding varies by breed, with some dogs shedding year-round in milder climates where seasonal temperature changes are less dramatic.

6 Signs of Abnormal Hair Loss

• Patchy or asymmetrical loss – Normal shedding occurs evenly across the body, while abnormal hair loss in dogs often appears in irregular patches or predominantly on one side.
• Skin inflammation or irritation – Redness, swelling, crusting, or scaling accompanying hair loss suggests an underlying skin condition affecting the hair follicles.
• Changes in skin appearance – Darkened, thickened, or unusually colored skin beneath areas of hair loss can indicate chronic inflammation or hormonal issues.
• Excessive itching or discomfort – If your dog is constantly scratching, biting, or rubbing areas with hair loss, this points to irritation rather than normal shedding.
• Circular or ring-shaped patterns – These distinctive patterns often suggest fungal infections like ringworm affecting the hair follicles.
• Hair that breaks easily or fails to regrow – When hair breaks off rather than falling out completely or doesn’t regrow in previously bare areas, this indicates damage to the hair shafts or follicles.

Common Causes of Hair Loss in Dogs

Parasites

Parasitic infestations are among the most common causes of hair loss in dogs, triggering both direct damage to hair follicles and secondary hair loss from intense scratching. These tiny invaders burrow into the skin or attach to hair follicles, causing inflammation, allergic reactions, and damage to the surrounding tissue. The resulting irritation prompts dogs to scratch, bite, and rub affected areas excessively, creating a cycle of trauma that accelerates hair loss in dogs. Left untreated, parasitic infestations can spread across the body and lead to secondary bacterial infections that further compromise skin health and hair growth.

4 Common Parasites that Cause Hair Loss in Dogs

• Mange mites (Demodex and Sarcoptes) – These microscopic mites burrow into the skin and hair follicles, causing intense itching, inflammation, and hair loss, typically beginning on the face, ears, and legs.
• Fleas – Beyond causing itching, many dogs develop flea allergy dermatitis, an allergic reaction to flea saliva that triggers intense inflammation and hair loss primarily along the back, tail base, and thighs.
• Ticks – While feeding on blood, ticks can cause localized irritation and hair loss at attachment sites, sometimes leaving small bald spots that persist even after the tick is removed.
• Lice – Though less common than other parasites, canine lice cause irritation and hair loss by attaching to hair shafts and feeding on skin debris or blood, typically affecting dogs in crowded or unsanitary conditions.

Allergies

Allergies represent a significant cause of hair loss in dogs, triggering immune system overreactions that manifest through skin inflammation and damage to hair follicles. When exposed to allergens, sensitive dogs experience an inflammatory cascade that disrupts normal skin barrier function and hair growth cycles. This inflammation leads to intense itching, prompting dogs to scratch, lick, and chew at affected areas, which further damages hair follicles and accelerates hair loss. Over time, chronic allergic inflammation can alter skin structure and function, creating persistent hair loss even during periods when allergen exposure is reduced.

5 Common Allergens that Cause Hair Loss in Dogs

• Environmental allergens – Pollen, mold, grass, and dust mites can trigger seasonal or year-round allergic reactions, causing hair loss, particularly on the paws, face, ears, and underside of the body where contact with these allergens is greatest.
• Food ingredients – Proteins such as chicken, beef, dairy, and eggs are common culprits in food allergies, leading to generalized itching and hair loss in dogs that doesn’t follow seasonal patterns and often affects the ears, paws, groin, and face.
• Flea saliva – Even a single flea bite can trigger severe allergic dermatitis in sensitive dogs, causing disproportionate inflammation, intense itching, and hair loss primarily along the back, tail base, and thighs.
• Contact allergens – Cleaning products, synthetic fabrics, plastic feeding bowls, and lawn chemicals can cause contact dermatitis with hair loss concentrated in areas that directly touch these substances, such as the belly, paws, and face.
• Dust mites – These microscopic creatures commonly found in bedding and carpeting can cause persistent allergic reactions, leading to chronic skin inflammation and progressive hair loss in areas where dogs rest frequently.

Medical Conditions

Underlying medical conditions often manifest through hair loss in dogs by disrupting normal hair growth cycles or compromising skin health. Systemic illnesses can affect hormone levels, immune function, and nutrient absorption, all of which play crucial roles in maintaining healthy hair follicles. These conditions typically cause gradual, progressive hair loss that may initially go unnoticed until significant thinning has occurred. Unlike parasite-related or allergic hair loss, medical causes often produce symmetrical patterns and may be accompanied by other symptoms like changes in energy, appetite, or water consumption.

3 Common Medical Conditions that Cause Hair Loss in Dogs

• Hypothyroidism – This hormonal disorder causes symmetrical hair thinning, typically starting on the tail and back legs, accompanied by weight gain, lethargy, and sensitivity to cold due to reduced thyroid hormone production affecting hair follicle function.
• Autoimmune disorders – Conditions like pemphigus and lupus cause the immune system to attack hair follicles and skin structures, resulting in crusting, scaling, and hair loss, typically beginning on the face, ears, and footpads.
• Cancer – Both skin cancers and internal malignancies can manifest as hair loss in dogs, either through direct involvement of skin and hair follicles or as a paraneoplastic syndrome where the body’s response to cancer affects distant tissues, including the skin.

Dietary Deficiencies

Dietary deficiencies can significantly impact hair health in dogs by depriving hair follicles of essential building blocks needed for growth and maintenance. Without adequate nutrition, the hair growth cycle becomes disrupted, leading to weak, brittle hair that breaks easily or falls out prematurely. Since hair growth is considered a non-essential function biologically, the body redirects limited nutrients to vital organs during nutritional shortages, making the coat one of the first areas to show signs of deficiency. Poor quality commercial foods, homemade diets without proper supplementation, or malabsorption issues can all contribute to nutrition-related hair loss in dogs.

5 Common Deficiencies that Cause Hair Loss in Dogs

• Protein insufficiency – As hair is primarily composed of protein (specifically keratin), inadequate protein intake leads to dull, brittle hair that breaks easily and falls out, creating a general thinning across the entire coat rather than patchy loss.
• Essential fatty acid deficiency – Omega-3 and Omega-6 fatty acids are crucial for skin barrier function and inflammation control; their shortage causes dry, flaky skin and hair that lacks luster, breaks easily, and falls out prematurely.
• Zinc deficiency – This essential mineral plays key roles in protein synthesis and cell division necessary for hair growth; its deficiency causes crusty skin lesions and hair loss, particularly around the face, ears, pressure points, and footpads.
• Vitamin A deficiency – This vitamin regulates keratin synthesis and sebum production; insufficient levels lead to dry, scaly skin and progressive hair thinning, particularly noticeable in fast-growing areas of the coat.
• B-vitamin complex deficiencies – These vitamins support cellular energy production and protein metabolism; their shortage results in dermatitis, scaly skin patches, and hair loss that often begins around the face and spreads to the body.

Stress

Stress can trigger hair loss in dogs through complex interactions between the nervous, endocrine, and immune systems that disrupt normal hair growth cycles. When dogs experience chronic stress, elevated cortisol levels can force hair follicles into a premature resting phase, preventing new hair growth while existing hairs continue to fall out. Additionally, stress often manifests through behavioral changes like excessive grooming, licking, or chewing that directly damages hair and skin. The body’s stress response also diverts resources away from “non-essential” functions like coat maintenance, leading to poorer hair quality and increased shedding.

4 Common Stressors that Cause Hair Loss in Dogs

• Household tension – Arguments, domestic conflict, or the presence of incompatible pets creates chronic stress that manifests as patchy hair loss from excessive licking, often concentrated on lower limbs and joints.
• Separation anxiety – Dogs with attachment issues may develop compulsive behaviors when left alone, resulting in self-inflicted hair loss from constant licking or chewing, typically in symmetric patterns on the front legs or flanks.
• Boredom and under-stimulation – Insufficient physical and mental exercise can lead to destructive self-soothing behaviors, causing focal areas of hair loss where dogs repeatedly lick or chew to release tension and frustration.
• Schedule disruptions – Changes in family routines, irregular feeding times, or inconsistent exercise patterns can elevate stress hormones, contributing to diffuse thinning of the coat as hair growth cycles become dysregulated.

How is Hair Loss in dogs treated?

Conclusion

Hair loss in dogs can range from a minor, temporary issue to a sign of serious underlying health concerns affecting the skin and hair follicles. By understanding the various causes—from seasonal shedding and dust mites to hormonal imbalances and stress—pet owners can better partner with veterinarians to identify and address the root problems. Early intervention often leads to better outcomes, making it crucial to seek professional guidance when abnormal hair loss occurs.

For comprehensive diagnostics and effective treatment plans tailored to your pet’s specific hair loss condition, schedule an appointment with our experienced team at Harvester Animal Clinic in St. Peters, MO. We provide expert dermatological care for all breeds and coat types. For more tips on maintaining your pet’s coat health and updates on the latest treatments, follow us on Facebook and Instagram, where we regularly share valuable pet care information.