Hair Loss and Alopecia
Category: symptoms
Hair loss (alopecia) in dogs and cats can be localized or widespread, and may occur with or without itching. The pattern, distribution, and accompanying symptoms provide important clues about the underlying cause. While some causes are cosmetic, others indicate serious systemic disease requiring treatment.
## Types of Hair Loss
**Symmetric bilateral alopecia:** Hair loss that appears evenly on both sides of the body. Often indicates hormonal or endocrine disorders. Non-itchy.
**Focal/patchy hair loss:** One or a few distinct areas of hair loss. Common in ringworm, bacterial infections, and demodex mange.
**Diffuse thinning:** Overall thinning of the coat without distinct bald patches. Can indicate nutritional deficiencies, systemic illness, or telogen effluvium.
**Self-induced alopecia:** Hair loss caused by the pet scratching, licking, chewing, or pulling out its own hair. Indicates pruritus (itching) or behavioral issues.
## Common Causes
**Parasitic:** Demodectic mange — causes focal to generalized hair loss, often starting on the face in young dogs. Sarcoptic mange — intense itching and hair loss on ears, elbows, and belly. Flea allergy dermatitis — hair loss on the lower back and tail base. Ear mites — hair loss around ears from scratching.
**Infectious:** Ringworm (dermatophytosis) — circular patches of hair loss, may have central scaling. Highly contagious to other animals and humans. Bacterial skin infections (pyoderma) — often secondary to other conditions.
**Hormonal/Endocrine:** Hypothyroidism (dogs) — bilateral symmetric hair loss, especially on the trunk, tail ("rat tail"), and nose. Coat becomes thin, dry, and dull. Cushings disease (hyperadrenocorticism) — symmetric hair loss on trunk, thin skin, pot-bellied appearance, increased drinking and urination. Sex hormone imbalances — alopecia in intact or recently neutered animals. Seasonal flank alopecia — non-itchy symmetric hair loss on flanks, often seasonal.
**Allergic:** Atopic dermatitis, food allergy, and contact allergy — hair loss in these cases is self-induced from scratching and licking.
**Behavioral:** Psychogenic alopecia — compulsive licking or barbering, more common in cats. Often related to stress, anxiety, or boredom. The hair is actually present but broken off, distinguishing it from true alopecia.
**Nutritional:** Zinc deficiency, essential fatty acid deficiency, and protein deficiency can all cause poor coat quality and hair loss.
**Autoimmune:** Pemphigus, lupus, and alopecia areata — relatively uncommon but can cause distinctive patterns of hair loss.
## When to See a Vet
Schedule a veterinary visit if hair loss is progressive or spreading, there are bald patches with redness, scaling, or crusting, your pet is excessively itching, licking, or scratching, hair loss is accompanied by increased drinking, urination, or appetite changes, the skin appears thickened, darkened, or infected, or multiple pets or family members are also showing skin changes (possible contagious cause).
## Diagnosis
Your veterinarian may recommend skin scraping for mites, fungal culture or Wood lamp examination for ringworm, skin cytology for infection identification, blood work including thyroid and cortisol testing, skin biopsy for complex cases, elimination diet trial if food allergy is suspected, and trichogram (microscopic hair examination) to determine if hair is falling out vs being pulled out.
## Treatment
Treatment is directed at the underlying cause. Parasitic causes are treated with appropriate antiparasitic medications. Infections require antimicrobial therapy (antibiotics, antifungals). Hormonal conditions need specific hormone replacement or regulation. Allergic conditions benefit from allergen avoidance, immunotherapy, and symptomatic management. Behavioral causes may require environmental enrichment, stress reduction, and sometimes behavioral medications.
## Diagnostic Approach to Hair Loss
Your veterinarian will follow a systematic diagnostic protocol to identify the underlying cause:
**Skin scraping:** Deep skin scrapings look for Demodex mites (demodectic mange), which burrow deep into hair follicles. Superficial scrapings detect Sarcoptes mites (sarcoptic mange).
**Fungal culture (DTM):** The gold standard for diagnosing dermatophytosis (ringworm). Results take 7-14 days. Woods lamp examination (UV light) can provide preliminary screening but only detects approximately 50% of ringworm species.
**Hormone testing:** Thyroid panel (T4, free T4, TSH) for suspected hypothyroidism in dogs. ACTH stimulation test or low-dose dexamethasone suppression test for suspected Cushings disease. Estrogen and testosterone levels if sex hormone-related alopecia is suspected.
**Skin biopsy:** Essential for diagnosing autoimmune diseases (alopecia areata, pemphigus), color dilution alopecia, follicular dysplasia, and sebaceous adenitis. A dermatopathologist provides the most accurate interpretation.
## Treatment Approaches by Cause
Treatment varies dramatically based on diagnosis: hypothyroid alopecia responds to daily levothyroxine supplementation (hair regrowth typically visible within 2-3 months). Allergic alopecia requires allergen management plus itch control with Apoquel or Cytopoint. Ringworm requires systemic antifungal medication (itraconazole or terbinafine) for 6-8 weeks plus environmental decontamination. Cushings disease management depends on cause — medical (trilostane) or surgical (adrenalectomy). Psychogenic alopecia (over-grooming from stress) requires environmental enrichment, stress reduction, and sometimes anti-anxiety medication.
*Written by PetNurse Clinical Team · Sources: AVMA, ACVD Dermatology, Merck Veterinary Manual*
## Types of Hair Loss
**Symmetric bilateral alopecia:** Hair loss that appears evenly on both sides of the body. Often indicates hormonal or endocrine disorders. Non-itchy.
**Focal/patchy hair loss:** One or a few distinct areas of hair loss. Common in ringworm, bacterial infections, and demodex mange.
**Diffuse thinning:** Overall thinning of the coat without distinct bald patches. Can indicate nutritional deficiencies, systemic illness, or telogen effluvium.
**Self-induced alopecia:** Hair loss caused by the pet scratching, licking, chewing, or pulling out its own hair. Indicates pruritus (itching) or behavioral issues.
## Common Causes
**Parasitic:** Demodectic mange — causes focal to generalized hair loss, often starting on the face in young dogs. Sarcoptic mange — intense itching and hair loss on ears, elbows, and belly. Flea allergy dermatitis — hair loss on the lower back and tail base. Ear mites — hair loss around ears from scratching.
**Infectious:** Ringworm (dermatophytosis) — circular patches of hair loss, may have central scaling. Highly contagious to other animals and humans. Bacterial skin infections (pyoderma) — often secondary to other conditions.
**Hormonal/Endocrine:** Hypothyroidism (dogs) — bilateral symmetric hair loss, especially on the trunk, tail ("rat tail"), and nose. Coat becomes thin, dry, and dull. Cushings disease (hyperadrenocorticism) — symmetric hair loss on trunk, thin skin, pot-bellied appearance, increased drinking and urination. Sex hormone imbalances — alopecia in intact or recently neutered animals. Seasonal flank alopecia — non-itchy symmetric hair loss on flanks, often seasonal.
**Allergic:** Atopic dermatitis, food allergy, and contact allergy — hair loss in these cases is self-induced from scratching and licking.
**Behavioral:** Psychogenic alopecia — compulsive licking or barbering, more common in cats. Often related to stress, anxiety, or boredom. The hair is actually present but broken off, distinguishing it from true alopecia.
**Nutritional:** Zinc deficiency, essential fatty acid deficiency, and protein deficiency can all cause poor coat quality and hair loss.
**Autoimmune:** Pemphigus, lupus, and alopecia areata — relatively uncommon but can cause distinctive patterns of hair loss.
## When to See a Vet
Schedule a veterinary visit if hair loss is progressive or spreading, there are bald patches with redness, scaling, or crusting, your pet is excessively itching, licking, or scratching, hair loss is accompanied by increased drinking, urination, or appetite changes, the skin appears thickened, darkened, or infected, or multiple pets or family members are also showing skin changes (possible contagious cause).
## Diagnosis
Your veterinarian may recommend skin scraping for mites, fungal culture or Wood lamp examination for ringworm, skin cytology for infection identification, blood work including thyroid and cortisol testing, skin biopsy for complex cases, elimination diet trial if food allergy is suspected, and trichogram (microscopic hair examination) to determine if hair is falling out vs being pulled out.
## Treatment
Treatment is directed at the underlying cause. Parasitic causes are treated with appropriate antiparasitic medications. Infections require antimicrobial therapy (antibiotics, antifungals). Hormonal conditions need specific hormone replacement or regulation. Allergic conditions benefit from allergen avoidance, immunotherapy, and symptomatic management. Behavioral causes may require environmental enrichment, stress reduction, and sometimes behavioral medications.
## Diagnostic Approach to Hair Loss
Your veterinarian will follow a systematic diagnostic protocol to identify the underlying cause:
**Skin scraping:** Deep skin scrapings look for Demodex mites (demodectic mange), which burrow deep into hair follicles. Superficial scrapings detect Sarcoptes mites (sarcoptic mange).
**Fungal culture (DTM):** The gold standard for diagnosing dermatophytosis (ringworm). Results take 7-14 days. Woods lamp examination (UV light) can provide preliminary screening but only detects approximately 50% of ringworm species.
**Hormone testing:** Thyroid panel (T4, free T4, TSH) for suspected hypothyroidism in dogs. ACTH stimulation test or low-dose dexamethasone suppression test for suspected Cushings disease. Estrogen and testosterone levels if sex hormone-related alopecia is suspected.
**Skin biopsy:** Essential for diagnosing autoimmune diseases (alopecia areata, pemphigus), color dilution alopecia, follicular dysplasia, and sebaceous adenitis. A dermatopathologist provides the most accurate interpretation.
## Treatment Approaches by Cause
Treatment varies dramatically based on diagnosis: hypothyroid alopecia responds to daily levothyroxine supplementation (hair regrowth typically visible within 2-3 months). Allergic alopecia requires allergen management plus itch control with Apoquel or Cytopoint. Ringworm requires systemic antifungal medication (itraconazole or terbinafine) for 6-8 weeks plus environmental decontamination. Cushings disease management depends on cause — medical (trilostane) or surgical (adrenalectomy). Psychogenic alopecia (over-grooming from stress) requires environmental enrichment, stress reduction, and sometimes anti-anxiety medication.
*Written by PetNurse Clinical Team · Sources: AVMA, ACVD Dermatology, Merck Veterinary Manual*
Source: Merck Veterinary Manual; Veterinary Dermatology Journal; AAHA Dermatology Guidelines