Dermatitis
Inflammation of the skin, presenting as redness, itching, scaling, or lesions. Dermatitis is a descriptive term with many possible causes including allergies, infections, parasites, and immune-mediated disease.
Dermatitis literally means “inflammation of the skin” (from Greek derma, “skin” + -itis, “inflammation”). It is a descriptive term, not a specific diagnosis — many different conditions can cause dermatitis, and effective treatment requires identifying the underlying trigger.
Common Types in Dogs
Allergic Dermatitis
The most common category overall:
- Atopic dermatitis: allergic reaction to environmental allergens (pollens, dust mites, mold). Typically causes itching on the face, ears, paws, and ventral surfaces. Often seasonal initially, then may become year-round.
- Food allergy dermatitis: adverse reaction to dietary proteins. Causes year-round itching, often involving the ears, paws, and perianal area. Diagnosis requires a strict elimination diet trial.
- Flea allergy dermatitis: hypersensitivity to flea saliva. Even a single flea bite can trigger intense itching, particularly over the rump, tail base, and caudal thighs.
- Contact dermatitis: reaction to substances contacting the skin (cleaning products, certain plants, topical medications). Typically affects areas with thin hair or direct contact points.
Infectious Dermatitis
- Bacterial pyoderma: secondary bacterial skin infection, often following allergic or parasitic skin disease. Staphylococcus pseudintermedius is the most common pathogen.
- Fungal dermatitis: dermatophytosis (ringworm), Malassezia dermatitis (yeast overgrowth, particularly in skin folds and ears).
- Parasitic dermatitis: demodectic mange (Demodex mites), sarcoptic mange (Sarcoptes scabiei), and other ectoparasites.
Immune-Mediated Dermatitis
- Pemphigus: autoimmune blistering diseases targeting the skin
- Discoid lupus erythematosus: autoimmune condition affecting the nasal planum
- Sebaceous adenitis: immune-mediated destruction of sebaceous glands
Diagnostic Approach
Because dermatitis has so many potential causes, a systematic diagnostic approach is essential:
- Detailed history: onset, seasonality, distribution, response to prior treatments, diet, flea control, environmental exposure
- Physical examination: distribution pattern, lesion type, secondary changes
- Skin cytology: identifies bacteria, yeast, and inflammatory cells
- Skin scraping: detects mites (Demodex, Sarcoptes)
- Fungal culture: for suspected dermatophytosis
- Elimination diet trial: for suspected food allergy (8-12 weeks)
- Allergy testing: intradermal or serum testing for environmental allergens
- Biopsy: for atypical, non-responsive, or suspected immune-mediated cases
Treatment Principles
Treating dermatitis effectively requires addressing the cause, not just the symptoms. Symptomatic anti-itch therapy (steroids, Apoquel, Cytopoint) provides relief but does not resolve the underlying problem. Identifying and managing the trigger — whether allergic, infectious, or immune-mediated — determines long-term control.