Dermatitis in Animals

Inflammation of the skin can be produced by numerous agents, including external irritants, burns, allergens, trauma, and infection (bacterial, viral, parasitic, or fungal). Inflammation can be associated with concurrent internal or systemic disease. Hereditary factors can also be involved. Allergies form an important group of etiological factors, especially in small animals.

The skin’s response to insult is generically called dermatitis and manifests as any combination of pruritus, scaling, erythema, lichenification (increased thickening and hyperpigmentation of the skin), hyperpigmentation, oily seborrhea, odor, and alopecia.

In the usual progression of skin disease, an underlying trigger (disease syndrome) causes primary lesions, such as papules, pustules, and vesicles (see Diagnosis of Skin Diseases in Small Animals).

Pruritus is common in many skin diseases, and, in conditions that are not inherently pruritic, it is often present because of secondary infections or as a result of production of inflammatory mediators. As inflammatory changes progress, crusting and scaling develop. If the process involves the deeper dermis, exudation, pain, and sloughing of the skin can occur.

Secondary bacterial and yeast infections commonly develop as a result of skin inflammation. As dermatitis becomes chronic, acute signs of inflammation (eg, erythema) subside, and primary lesions become obscured by signs of chronic inflammation (skin thickening, hyperpigmentation, scaling, seborrhea). Often the skin becomes drier; if pruritus is not a component of the underlying trigger, it often develops at this stage.

Resolution of dermatitis requires identification of the underlying cause and treatment of secondary infections or other complications.