Shedding is one of the most common concerns reported by cat and dog owners. The hair cycle is a normal physiologic process, and seasonal shedding can be completely normal. However, excessive, diffuse, or focal hair loss (alopecia) may indicate an underlying dermatologic, endocrine, nutritional, or systemic disorder. Coat quality is often a visible reflection of general health and nutritional status. This article explains how to distinguish normal shedding from pathologic hair loss, reviews the main causes of alopecia, outlines the diagnostic approach, and presents strategies for nutritional management of coat health.
Hair-Loss Findings That Require Veterinary Assessment
- Patchy or focal alopecia, whether symmetric or asymmetric
- Hair loss with itching, especially if the skin is red, crusted, or ulcerated
- Skin lesions such as scaling, pustules, blackheads, lichenification, or marked dandruff
- Bilateral symmetric alopecia, raising suspicion of endocrine disease
- Excessive licking or chewing, particularly in cats
- Bad odour, suggesting secondary bacterial or yeast infection
- Systemic signs such as weight loss, polyuria, lethargy, or appetite change
1. The Hair Cycle: Normal Physiology
Phases of Hair Growth
- Anagen: Active growth phase, with breed-dependent duration
- Catagen: Transitional phase as the follicle regresses
- Telogen: Resting phase, in which the hair remains in place but no longer grows
- Exogen: Shedding phase, when the old hair falls out and a new anagen cycle begins
Factors That Influence Shedding
- Photoperiod: Length of daylight is the main natural driver
- Temperature: Important, but secondary
- Indoor living: Artificial light disrupts seasonal cycling and may cause year-round shedding
- Breed: Double-coated breeds shed heavily; continuously growing coats shed less visibly
- Hormones: Estrogen, thyroid hormones, and cortisol influence the cycle
- Nutrition: Protein, fatty acids, zinc, and biotin directly affect coat quality
2. Normal vs Abnormal Shedding
| Feature | Normal (Physiologic) | Abnormal (Pathologic) |
|---|---|---|
| Distribution | Diffuse and homogeneous over the whole body | Focal, patchy, symmetric, or asymmetric |
| Skin appearance | Healthy-looking skin | Redness, scale, crusting, lesions, thickening, or hyperpigmentation |
| Pruritus | Absent | Often present in allergic, parasitic, or infectious disease |
| Coat quality | Shed hairs look normal and regrowth occurs | Hair may be brittle, dull, dry, and regrowth may be poor |
| Seasonality | Usually peaks in spring and autumn | Occurs year-round or progressively worsens |
| General health | The animal otherwise looks healthy | Changes in body weight, appetite, or energy may accompany the coat problem |
3. Causes of Abnormal Hair Loss
3.1 Pruritic Alopecia
| Cause | Typical Features | Species |
|---|---|---|
| Flea allergy dermatitis | Most common cause; tail base, dorsum, and ventrum are common sites; severe itching; even a few flea bites can trigger it | Cat & Dog |
| Atopic dermatitis | Environmental allergens such as dust, pollen, or mold; often affects face, ears, feet, and axillae; chronic and recurrent | Common in dogs; also seen in cats |
| Food allergy | Non-seasonal, often involving face, ears, or perineal region; diagnosed with an elimination diet | Cat & Dog |
| Sarcoptic mange | Intense itching, especially on ear margins, elbows, and chest; crusting; zoonotic concern | Dog |
| Dermatophytosis | Ring-shaped lesions with scale and broken hairs; pruritus may be minimal | Common in cats; also occurs in dogs |
| Malassezia dermatitis | Greasy, malodorous skin, often affecting folds and warm moist areas | Common in dogs |
3.2 Non-pruritic Alopecia
| Cause | Typical Features | Species |
|---|---|---|
| Hypothyroidism | Bilateral symmetric alopecia, “rat tail,” obesity, lethargy, and bradycardia | Dog |
| Hyperadrenocorticism | Symmetric truncal alopecia, thin skin, pot belly, polyuria/polydipsia, and sometimes calcinosis cutis | Dog |
| Hyperthyroidism | Poor, unkempt coat with increased shedding and weight loss | Cat |
| Alopecia X | Symmetric truncal alopecia with otherwise healthy skin, especially in Pomeranians and other Nordic breeds | Dog |
| Demodicosis | Localized or generalized hair loss due to Demodex mites; more common in young dogs or immunosuppressed animals | Common in dogs; less common in cats |
| Telogen effluvium | Diffuse shedding after stress, illness, surgery, or parturition; usually temporary | Cat & Dog |
| Nutritional deficiency | Protein, fatty-acid, zinc, or biotin deficiency causing a dry, brittle, dull coat | Cat & Dog |
3.3 Psychogenic Alopecia in Cats
Over-grooming in Cats
Cats with hair loss on the abdomen, inner thighs, or tail are often labelled as having psychogenic alopecia, but studies suggest that most cases still have an underlying medical cause such as allergy, parasites, or pain. Psychogenic alopecia is therefore a diagnosis of exclusion. Cats may over-groom secretly, leaving the skin apparently normal while the hairs are shortened or absent.
4. Diagnostic Approach
| Step | Test | Purpose |
|---|---|---|
| 1. History | — | Assess onset, duration, seasonality, itch, diet, parasite prevention, and stress |
| 2. Physical examination | Skin and coat assessment | Evaluate distribution of alopecia, skin lesions, parasites, and body condition |
| 3. Trichogram | Microscopic hair examination | Identify anagen/telogen hairs, broken shafts from licking, or ectothrix spores |
| 4. Skin scrapings | Superficial and deep scrapings | Detect Demodex, Sarcoptes, or Cheyletiella |
| 5. Wood’s lamp | UV screening | Some strains of Microsporum canis fluoresce; a negative result does not exclude infection |
| 6. Fungal culture | Dermatophyte test medium | Gold standard for ringworm diagnosis, typically requiring 7-14 days |
| 7. Blood testing | T4, cortisol, CBC, biochemistry | Screen for endocrine or systemic disease |
| 8. Elimination diet | 8-12 week diet trial | Diagnose food allergy using novel-protein or hydrolysed diets |
| 9. Skin biopsy | Histopathology | Used in atypical cases, autoimmune disease, neoplasia, or alopecia X |
5. Breed-Specific Shedding Patterns
Dog Breeds
- Heavy shedders: Siberian Husky, Alaskan Malamute, German Shepherd, Golden Retriever, and Labrador are double-coated breeds with intense seasonal coat blow
- Low shedders: Poodle, Bichon Frise, Maltese, and Shih Tzu have continuously growing coats and require grooming rather than heavy deshedding
- Hypothyroidism-prone breeds: Golden Retriever, Doberman, and Irish Setter
- Alopecia X: Especially Pomeranian, Chow Chow, and Keeshond
- Colour dilution alopecia: Seen in blue or dilute-coated Dobermans and Italian Greyhounds
Cat Breeds
- Heavy shedders: Persian, Maine Coon, Ragdoll, and British Shorthair have abundant undercoat
- Low shedders: Sphynx, Devon Rex, Cornish Rex, and Siamese
- Dermatophytosis-prone: Persian and Himalayan cats with long, dense coats
- Psychogenic grooming tendency: Siamese, Birman, and Burmese are often cited as anxiety-prone breeds
6. Nutrition and Coat Health: The VetKriter Approach
VetKriter Nutrition Principle
Hair is one of the fastest-growing tissues in the body and consumes a large share of dietary protein and essential fatty acids. In dogs, 25-30% of daily protein use may support skin and coat maintenance. Coat quality is therefore highly sensitive to diet, and a dull, dry, brittle coat often suggests a nutritional gap.
6.1 Nutrients Critical for Coat Health
| Nutrient | Skin/Coat Function | Signs of Deficiency | Common Sources |
|---|---|---|---|
| Protein | Keratin synthesis; hair is mostly protein | Dry, brittle, dull coat; slow regrowth; fading colour | Animal proteins such as poultry, fish, lamb, and egg |
| Omega-6 (linoleic acid) | Maintains epidermal integrity and sebaceous gland function | Dry skin, dandruff, greasy coat, delayed wound healing | Chicken fat, sunflower oil, corn oil |
| Omega-3 (EPA/DHA) | Anti-inflammatory support and improved coat shine | More severe inflammatory skin disease | Fish oil, salmon oil, krill oil |
| Zinc | Keratocyte proliferation, wound healing, epidermal renewal | Zinc-responsive dermatosis, scaling, crusting, alopecia | Red meat, zinc sulfate, chelated zinc |
| Biotin | Supports keratin structure and fatty-acid metabolism | Brittle hair and alopecia; deficiency is uncommon | Liver, egg yolk, supplementation |
| Vitamin A | Sebaceous-gland regulation and keratinocyte differentiation | Hyperkeratosis, poor coat quality; excess is also harmful | Liver, fish oil, beta-carotene for dogs |
| Vitamin E | Antioxidant protection and support during dermatitis | Skin lesions and panniculitis | Vegetable oils, tocopherols |
| Copper | Melanin production, coat colour, collagen cross-linking | Faded or reddish coat colour change | Organ meat, copper sulfate, chelated copper |
| Methionine + cysteine | Sulfur amino acids needed for keratin disulfide bonds | Weak hair structure and slow coat growth | Egg, meat, and fish |
6.2 The Omega-6 : Omega-3 Balance
Fatty-Acid Balance and Coat Health
Both omega-6 and omega-3 fatty acids are important for the skin and coat. Omega-6 supports the epidermal barrier, while omega-3 (EPA/DHA) helps reduce inflammation. A practical omega-6:omega-3 ratio of about 5:1 to 10:1 is often targeted. Many commercial diets provide adequate omega-6, but omega-3 may be relatively limited, so fish-oil supplementation can improve coat shine and skin comfort, especially in allergic dermatitis.
6.3 Diet Quality and Coat Health
Diet Features That Support Coat Health
- High animal-protein content: Supports keratin synthesis and sulfur amino-acid supply
- Balanced fat profile: Adequate omega-6 and omega-3 intake
- Fish or salmon oil: Practical sources of EPA and DHA
- Chelated zinc: Better bioavailability than some inorganic forms
- Biotin support: Helps maintain hair structure
- Antioxidants: Vitamin E and selenium help reduce oxidative stress
Factors That Harm Coat Health
- Low-quality protein: Plant-heavy diets with poor amino-acid profiles
- Too little fat: Can worsen dry skin and dull coat quality
- Rancid food: Oxidised fats increase vitamin E demand and may reduce palatability
- Raw egg white: Avidin binds biotin and may contribute to deficiency over time
- Excess vitamin A: Rare, but possible with inappropriate supplementation
- Unbalanced homemade diets: May lack zinc, copper, or biotin
7. Coat Care at Home
Regular Brushing
- Short-coated animals: Usually once or twice weekly with a curry or bristle brush
- Long-coated animals: Often require daily brushing with a slicker brush and metal comb
- Double-coated breeds: Need undercoat tools and more frequent grooming during seasonal coat blow
- Cats: Two to three sessions weekly is reasonable, while long-haired cats may need daily grooming
- Brushing also improves circulation and helps distribute natural skin oils
Bathing
- Dogs: Usually once or twice monthly is sufficient; excessive bathing removes natural oils
- Cats: Usually do not need routine bathing, except in selected long-haired or medical cases
- Shampoo choice: Veterinary shampoo is preferred; human shampoo should not be used
- Dermatologic disease: Medicated shampoos may be indicated depending on the condition
- Over-bathing: May worsen dryness and increase shedding
8. When Should You See the Veterinarian?
Usually Normal and Can Be Monitored
- Seasonal diffuse shedding in spring or autumn
- No itch and no skin lesions
- Good coat quality with visible regrowth
- The animal otherwise remains healthy and energetic
- The problem is manageable with regular brushing
Veterinary Assessment Is Needed
- Patchy or focal hair loss
- Itch, redness, crusting, or obvious irritation
- Symmetric truncal alopecia
- Pustules, ulcers, or thickened skin
- Strong odour suggesting infection
- Weight loss, excessive drinking, or other systemic signs
- Abdominal or medial-thigh alopecia in cats
9. References
- Miller WH, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology. 7th Ed. Elsevier. 2013.
- Watson TDG. Diet and skin disease in dogs and cats. J Nutr. 1998;128(12):2783S-2789S.
- Bauer JE. Therapeutic use of fish oils in companion animals. JAVMA. 2011;239(11):1441-1451.
- White SD. Food hypersensitivity in 30 dogs. JAVMA. 1986;188(7):695-698.
- Colombini S, et al. Feline symmetrical alopecia: A prospective study. JAAHA. 2001;37(5):411-415.
- FEDIAF Nutritional Guidelines for Complete and Complementary Pet Food. 2024.
- WSAVA Global Nutrition Committee. Nutritional Assessment Guidelines. 2024.