Why is my old dog losing hair? 10 causes and what to do

You're petting your old dog and you notice it. A patch of thin fur on their flank. Clumps of hair on the couch that seem like more than normal shedding. Maybe their once-thick coat has become sparse enough that you can see skin showing through. Or perhaps bald spots have appeared seemingly overnight, and you're wondering what happened.

Hair loss in senior dogs, also called alopecia, is common but never "normal." While some coat changes happen naturally with age, significant thinning, bald patches, or excessive shedding almost always point to an underlying cause that needs attention. The good news is that most causes of hair loss in older dogs are treatable once identified.

This guide covers the most common reasons your senior dog may be losing hair, what patterns to look for, when to see the vet, and what treatment options are available.

Normal aging vs. abnormal hair loss

Before we dive into medical causes, it helps to understand what's normal. As dogs age, some coat changes are expected:

• Graying around the muzzle, eyebrows, and chest
• A slightly thinner or less dense coat overall
• Coarser or drier texture compared to their younger years
• A more muted color or loss of luster
• Slightly increased shedding during seasonal changes

What is NOT normal and should be investigated:

• Bald patches or areas where skin is clearly visible
• Symmetrical hair loss on both sides of the body
• Red, inflamed, flaky, or crusty skin underneath thinning hair
• Excessive scratching, licking, or chewing at the coat
• Sudden or rapid hair loss over days or weeks
• Hair that falls out in clumps
• A foul smell coming from the skin
• Sores, bumps, or darkened skin in areas of hair loss

If your senior dog is experiencing any of these abnormal patterns, something medical is likely going on. Let's look at the most common causes.

10 common causes of hair loss in senior dogs

1. Hypothyroidism

Hypothyroidism is the single most common hormonal cause of hair loss in older dogs. The thyroid gland, located in the neck, produces hormones that regulate metabolism. When it underproduces (hypothyroidism), it affects nearly every system in the body, including the skin and coat.

Hypothyroidism-related hair loss has a characteristic pattern:

• Symmetrical thinning: Hair loss occurs evenly on both sides of the body, often starting on the flanks, chest, and belly
• "Rat tail": The tail loses its fur, becoming thin and rope-like. This is one of the most recognizable signs of hypothyroidism
• No itching: Unlike allergies or infections, hypothyroid hair loss typically doesn't cause scratching because the skin isn't irritated, it's just not growing hair properly
• Slow regrowth: Areas that are shaved for surgery or grooming are very slow to grow back
• Darkened skin: The skin beneath thinning hair may become hyperpigmented (darker than normal)

Other signs of hypothyroidism to watch for:

• Weight gain without increased food intake
• Lethargy and reduced interest in exercise
• Cold intolerance and seeking warm spots
• A dull, dry, or brittle coat
• Recurring skin infections
• A "tragic" or puffy facial expression due to fluid retention

Hypothyroidism is diagnosed with a simple blood test and treated with daily thyroid hormone replacement medication (levothyroxine). Most dogs show noticeable coat improvement within 4 to 8 weeks of starting treatment, and full coat regrowth typically occurs within 3 to 4 months. The medication is inexpensive and generally needed for the rest of the dog's life.

2. Cushing's disease (hyperadrenocorticism)

Cushing's disease causes the body to produce too much cortisol, the stress hormone. It's most common in dogs over age 8 and is one of the leading endocrine causes of hair loss in senior dogs. Certain breeds, including Poodles, Dachshunds, Beagles, Boston Terriers, and Boxers, are predisposed.

Cushing's-related hair loss typically shows:

• Symmetrical thinning on the trunk, flanks, and sides of the body
• Sparing the head and legs: The hair loss concentrates on the body while the head and extremities are less affected
• Thin, fragile skin: The skin becomes noticeably thinner, almost papery, and may bruise easily
• Calcinosis cutis: Hard, white or yellowish calcium deposits in the skin, particularly along the back, neck, or groin
• Recurrent skin infections: Cortisol suppresses the immune system, making the skin vulnerable to bacterial and fungal infections

Other hallmark signs of Cushing's disease:

• Dramatically increased thirst and urination (often the first sign owners notice)
• Ravenous appetite
• A pot-bellied appearance due to muscle wasting and fat redistribution
• Panting, even at rest
• Muscle weakness and exercise intolerance

Cushing's disease requires blood testing and sometimes abdominal ultrasound to diagnose. Treatment depends on the type: pituitary-dependent Cushing's (the most common form, about 85% of cases) is usually managed with medication like trilostane or mitotane. Adrenal-dependent Cushing's, caused by an adrenal tumor, may be treated surgically. With proper management, coat regrowth can occur over several months.

3. Allergies

Allergies are a leading cause of hair loss in dogs of all ages, and they can worsen or first appear in the senior years. The hair loss from allergies is usually secondary, meaning the dog loses hair because they're scratching, biting, and licking their skin excessively, not because the hair itself is falling out.

There are three main types of allergies that cause hair loss:

• Environmental allergies (atopic dermatitis): Reactions to pollen, dust mites, mold, or grass. These often cause itching on the face, ears, paws, belly, and armpits. You may notice your dog licking their feet until they turn reddish-brown from saliva staining
• Food allergies: True food allergies can cause chronic itching and hair loss, often concentrated around the ears, face, paws, and rear end. Common culprits include beef, chicken, dairy, wheat, and soy
• Flea allergy dermatitis: Some dogs are extremely allergic to flea saliva, and even a single flea bite can trigger intense itching and hair loss, typically over the base of the tail, lower back, and inner thighs. Senior dogs with compromised immune systems may be more susceptible

Signs that allergies are behind your dog's hair loss:

• Intense itching, scratching, biting, or licking
• Red, inflamed skin
• Hot spots (moist, raw areas from excessive licking)
• Recurring ear infections
• Hair loss that worsens seasonally (environmental allergies) or is constant (food allergies)
• Saliva staining on paws or other licked areas

Treatment involves identifying and avoiding the allergen when possible, along with medications to control itching. Modern options like Apoquel (oclacitinib) and Cytopoint (lokivetmab) are highly effective and well-tolerated by most senior dogs. Your vet may recommend a food elimination trial to rule out food allergies, or allergy testing to identify environmental triggers.

4. Skin infections (bacterial and fungal)

As dogs age, their immune system weakens, making them more vulnerable to skin infections. These infections often cause localized or widespread hair loss along with other skin changes.

Bacterial skin infections (pyoderma):

• Red, pus-filled bumps or pustules
• Circular areas of hair loss with a ring of scaly skin (often confused with ringworm)
• Crusty or flaky skin
• A musty or unpleasant odor
• Often secondary to another condition like allergies, Cushing's, or hypothyroidism

Fungal infections (including ringworm):

• Circular patches of hair loss with a red, raised border
• Scaly, crusty, or darkened skin
• May or may not be itchy
• Ringworm is contagious to other pets and humans, so prompt diagnosis matters

Yeast infections (Malassezia):

• Greasy, thickened skin with a distinctive musty or "corn chip" smell
• Hair loss and darkened skin, especially in skin folds, ears, and between toes
• Intense itching
• Often occurs alongside allergies or immune suppression

Your vet can diagnose skin infections through skin scraping, cytology (examining cells under a microscope), or fungal culture. Treatment typically involves topical or oral antibiotics for bacterial infections, antifungal medications for fungal infections, and medicated shampoos. Identifying and treating the underlying cause is crucial to prevent recurrence.

5. Mange (demodectic and sarcoptic)

Mange is caused by microscopic mites that live on or within the skin. While often thought of as a condition in puppies or strays, mange can affect senior dogs, particularly those with weakened immune systems.

Demodectic mange (Demodex):

• Demodex mites live naturally on most dogs in small numbers, but an aging or suppressed immune system can allow them to overpopulate
• Causes patchy hair loss, often starting on the face, legs, or trunk
• Skin may be red, scaly, or darkened but is typically not very itchy
• In senior dogs, generalized demodectic mange (spreading over large areas) can be a sign of an underlying immune issue like cancer, Cushing's disease, or immunosuppressive medication effects

Sarcoptic mange (scabies):

• Caused by Sarcoptes scabiei mites that burrow into the skin
• Causes intense, relentless itching, often considered the itchiest condition in dogs
• Hair loss with crusty, thickened skin, typically starting on ear margins, elbows, hocks, and belly
• Highly contagious to other dogs and can temporarily infect humans

Mange is diagnosed through skin scrapings examined under a microscope. Modern treatment options, including isoxazoline flea and tick preventatives (like NexGard, Bravecto, or Simparica), are highly effective against both types of mange. In senior dogs with demodectic mange, your vet should also investigate why the immune system allowed the mite population to expand.

6. Seasonal flank alopecia

Some dogs develop a condition called seasonal flank alopecia, also known as cyclic flank alopecia, where they lose hair on one or both sides of their body during certain times of year, typically in late fall or winter when daylight hours decrease.

Characteristics of seasonal flank alopecia:

• Well-defined, symmetrical bald patches on the flanks (sides of the body)
• Skin underneath is usually darkly pigmented but otherwise healthy, no redness, itching, or scaling
• Hair typically regrows in spring or summer, though it may come back a different color or texture
• More common in certain breeds: Boxers, Bulldogs, Airedale Terriers, and Schnauzers
• Can occur at any age but may become more pronounced in senior dogs

Seasonal flank alopecia is considered a cosmetic issue that doesn't cause discomfort. No treatment is strictly necessary, though some veterinarians recommend melatonin supplementation, which has helped in some cases. The condition may recur annually with varying severity. It's important to distinguish this from hormonal causes like hypothyroidism or Cushing's disease, which require treatment.

7. Pressure sores and calluses

Senior dogs who spend more time lying down often develop pressure sores and calluses on bony prominences like elbows, hocks, and hips. These areas lose hair and develop thick, tough, sometimes cracked skin from repeated contact with hard surfaces.

While mild calluses are common and not dangerous, they can progress to:

• Hygromas: Fluid-filled swellings over pressure points, particularly the elbows
• Infected sores: Cracked calluses can allow bacteria to enter, causing painful infections
• Deep ulceration: In bedridden senior dogs, prolonged pressure can cause tissue breakdown similar to bed sores in humans

Prevention and management:

• Provide thick, supportive orthopedic beds
• Keep the callused areas clean and moisturized with pet-safe balms
• Encourage your dog to shift positions regularly
• Place padding in your dog's favorite resting spots
• If calluses become infected, cracked, or bleeding, see your vet for treatment

8. Skin tumors and growths

Senior dogs are prone to various skin growths, and some of these can cause localized hair loss. While many are benign, any new lump that causes hair loss should be evaluated by a veterinarian.

Common skin growths in senior dogs:

• Lipomas: Benign fatty tumors that are soft and moveable. Very common in older dogs, especially overweight ones. They generally don't cause hair loss unless they grow large enough to stretch the overlying skin
• Sebaceous adenomas: Benign growths of the oil glands that appear as small, wart-like bumps. Common in senior dogs, especially Poodles, Cocker Spaniels, and Miniature Schnauzers
• Mast cell tumors: These cancerous growths can appear as raised, hairless lumps that may be red, ulcerated, or fluctuate in size. They are the most common malignant skin tumor in dogs
• Squamous cell carcinoma: Often appears as a firm, raised, ulcerated mass. More common in dogs with light-colored or thin-haired skin, particularly on sun-exposed areas
• Melanoma: Darkly pigmented tumors that can appear on the skin, in the mouth, or on nail beds

Any new skin growth on a senior dog should be examined by your veterinarian. A fine needle aspirate, a quick, minimally invasive procedure where cells are collected with a small needle, can often determine whether a growth is benign or potentially cancerous. Early detection of malignant tumors significantly improves treatment outcomes.

9. Poor nutrition

A dog's coat is a direct reflection of their nutritional status. The skin and hair follicles require a constant supply of nutrients to maintain a healthy coat, and deficiencies can lead to noticeable hair loss, dullness, and thinning.

Nutritional factors that affect coat health:

• Essential fatty acid deficiency: Omega-3 and omega-6 fatty acids are critical for skin and coat health. Dogs who don't get enough may develop dry, flaky skin and a thin, brittle coat
• Protein deficiency: Hair is made primarily of protein (keratin). Senior dogs who aren't getting enough quality protein may experience thinning hair, slow regrowth, and dull coat texture
• Zinc deficiency: Zinc is essential for skin cell turnover and hair growth. Some breeds, particularly Huskies and Malamutes, are prone to zinc-responsive dermatosis
• Vitamin deficiencies: Low levels of biotin, vitamin A, or vitamin E can contribute to poor coat quality
• Poor digestion: Senior dogs with digestive issues may not absorb nutrients properly even from a good diet, leading to secondary nutritional deficiencies

If nutritional deficiency is suspected, your vet may recommend blood work to check nutrient levels and a diet review. Switching to a high-quality senior food formulated for skin and coat health, along with an omega-3 fatty acid supplement (fish oil), often produces visible improvement within 6 to 8 weeks.

10. Stress and anxiety

Just like in humans, chronic stress can take a physical toll on a dog's body, including their coat. Senior dogs may experience increased anxiety due to cognitive decline, sensory loss, pain, changes in household routine, or separation anxiety, and this stress can manifest as hair loss.

Stress-related hair loss in senior dogs often appears as:

• Psychogenic alopecia: Compulsive licking or chewing at a specific area (often the foreleg, flank, or base of tail) that results in a bald, sometimes raw patch. This is called an acral lick granuloma when it creates a thickened, raised lesion
• Generalized thinning: Chronic stress elevates cortisol levels naturally, which over time can cause the same type of hair loss seen in Cushing's disease
• Excessive shedding: Many dogs "blow" their coat when stressed, shedding far more than normal

Common stressors for senior dogs:

• Changes in routine or environment (moving, new family members, renovation)
• Loss of a companion animal or family member
• Untreated pain or illness
• Cognitive dysfunction causing confusion and anxiety
• Separation anxiety, which can develop or worsen with age

Addressing the underlying stressor is key. This may involve pain management, anti-anxiety medication, environmental enrichment, maintaining a consistent routine, or behavioral support. Your vet can help determine whether the licking or chewing is truly behavioral or if there's an underlying medical component driving it.

Patterns that help identify the cause

The location and pattern of your dog's hair loss can provide valuable clues about the underlying cause. Share these observations with your veterinarian.

• Symmetrical hair loss on both flanks: Hormonal causes (hypothyroidism, Cushing's disease, seasonal flank alopecia)
• Patchy, irregular hair loss: Infections (bacterial, fungal, or parasitic)
• Hair loss around the tail base and lower back: Flea allergy dermatitis
• Hair loss on the face, ears, and paws: Environmental allergies or demodectic mange
• Hair loss over bony prominences (elbows, hocks): Pressure sores and calluses
• Hair loss around a single lump or growth: Skin tumor
• Thinning tail ("rat tail"): Hypothyroidism
• Hair loss with pot-bellied appearance: Cushing's disease
• Hair loss in an area the dog obsessively licks: Pain, anxiety, or allergies
• Generalized thinning without specific patches: Nutritional deficiency, aging, or systemic illness

When to See the Vet

Any significant hair loss in a senior dog warrants a veterinary visit. While some causes are minor, others indicate serious underlying conditions that need treatment. Schedule an appointment if your dog:

• Has developed bald patches or areas of notably thinning fur
• Is scratching, licking, or chewing excessively
• Has red, inflamed, crusty, or foul-smelling skin
• Has developed new lumps or bumps where hair has fallen out
• Is losing hair along with other symptoms like weight gain, increased thirst, lethargy, or appetite changes
• Has a shaved area that hasn't regrown after several months

Seek prompt veterinary care if:

• The hair loss is spreading rapidly
• The skin is broken, bleeding, or oozing
• Your dog seems painful, feverish, or lethargic
• You notice a new growth that is ulcerated, rapidly growing, or changing in appearance

What to expect at the vet

Your veterinarian will take a systematic approach to determine the cause of your dog's hair loss. Be prepared for:

• Detailed history: When the hair loss started, whether it's itchy, any other symptoms, current diet and medications, flea prevention status, and any recent changes in the household
• Physical examination: Thorough skin examination including looking at the pattern of hair loss, skin condition, and checking for lumps, fleas, or skin lesions
• Skin scraping: Scraping the surface of affected skin to check for mites under the microscope
• Cytology: Pressing a microscope slide or piece of tape against affected skin to look for bacteria, yeast, or abnormal cells
• Fungal culture: Testing for ringworm by culturing hair or skin samples
• Blood work: Complete blood count, chemistry panel, thyroid testing, and possibly cortisol testing to check for hypothyroidism, Cushing's disease, or other systemic conditions
• Skin biopsy: In difficult cases, a small sample of skin may be sent to a pathologist for definitive diagnosis
• Fine needle aspirate: If a growth is present, cells may be collected for analysis

Treatment options

Treatment depends on the underlying cause. In many cases, addressing the root issue leads to significant coat improvement over time.

• Hypothyroidism: Daily levothyroxine medication. Coat improvement typically begins within 4 to 8 weeks, with full regrowth in 3 to 4 months
• Cushing's disease: Trilostane or mitotane to control cortisol production. Hair regrowth may take several months as the body rebalances
• Allergies: Allergen avoidance, anti-itch medications (Apoquel, Cytopoint), medicated baths, and omega-3 supplementation. Food allergies require a strict elimination diet trial
• Skin infections: Antibiotics for bacterial infections, antifungals for fungal infections, and medicated shampoos. Treatment of the underlying predisposing condition is essential
• Mange: Isoxazoline medications (NexGard, Bravecto, Simparica) are typically the first-line treatment and are highly effective
• Nutritional deficiency: Diet change to a high-quality senior food, omega-3 fatty acid supplementation, and targeted nutrient supplementation as recommended by your vet
• Skin tumors: Surgical removal for concerning growths. Benign growths may be monitored without treatment if they're not causing problems
• Stress-related: Address the underlying stressor, anti-anxiety medication if needed, environmental enrichment, and management of concurrent conditions

Supporting your senior dog's coat health at home

While medical treatment addresses the root cause, there are things you can do at home to support your senior dog's skin and coat health:

• Feed a high-quality diet: Look for senior dog foods with quality animal protein as the first ingredient and added omega fatty acids for skin support
• Add omega-3 supplements: Fish oil (EPA and DHA) provides powerful anti-inflammatory benefits for the skin. Ask your vet about the right dose for your dog's size
• Regular gentle grooming: Brushing stimulates blood flow to the skin and distributes natural oils. Use a soft brush appropriate for your dog's coat type, and be gentle over any thin or sensitive areas
• Don't over-bathe: Bathing too frequently strips natural oils and can worsen dry skin. Unless medicated baths are prescribed, once or twice a month is usually sufficient. Use a gentle, moisturizing dog shampoo
• Maintain flea prevention: Year-round flea prevention is essential, even for indoor dogs. A single flea can trigger an allergic response
• Provide comfortable bedding: Soft, padded beds reduce pressure sore formation and protect sensitive skin
• Keep the environment humidified: Dry indoor air, especially during winter with heating systems running, can worsen skin dryness and coat problems
• Monitor and document changes: Take photos of any bald patches or skin changes over time. This helps your vet track whether the condition is improving, stable, or worsening

Frequently asked questions

Is it normal for old dogs to lose hair?

Some mild coat thinning and texture changes are normal with aging. However, significant hair loss, bald patches, and excessive shedding are not simply "old age" and almost always indicate a treatable underlying condition. Don't dismiss hair loss as normal aging without having your vet evaluate it.

Can my old dog's hair grow back?

In most cases, yes. Once the underlying cause is identified and treated, hair typically regrows over weeks to months depending on the condition. Hormonal imbalances like hypothyroidism respond especially well to treatment, with most dogs achieving a full, healthy coat again. The main exceptions are permanent scarring from severe infections or surgery sites, and in some cases of long-standing Cushing's disease where skin changes may persist.

Should I give my senior dog supplements for hair loss?

Omega-3 fatty acid supplements (fish oil) are generally safe and beneficial for skin and coat health in senior dogs. However, supplements alone won't resolve hair loss caused by hormonal imbalances, infections, or other medical conditions. Think of supplements as supportive care alongside proper veterinary diagnosis and treatment, not a replacement for it.

Is my senior dog's hair loss contagious?

Most causes of hair loss in senior dogs, such as hypothyroidism, Cushing's disease, allergies, and age-related changes, are not contagious. However, ringworm and sarcoptic mange (scabies) are contagious to other pets and can temporarily affect humans. If your dog has patchy hair loss and other pets or family members are developing skin issues, see your vet promptly for diagnosis.

Hair loss in a senior dog is your body's way of sending a signal that something needs attention. It might be something as straightforward as a thyroid imbalance that's easily corrected with a daily pill, or it might be a clue to a more complex condition that needs care. Either way, your old dog deserves to have it investigated. With proper diagnosis and treatment, most senior dogs can regain a healthier coat and feel more comfortable in their own skin. If you've noticed changes in your dog's coat, don't wait. A visit to your veterinarian is the first step toward answers and, in most cases, a good outcome.