Small Animal Dermatology, 3rd edition

chapter 16 Contact Dermatitis....................................

DEFINITION/OVERVIEW

Irritant contact dermatitis (ICD) and allergic contact dermatitis (ACD) are two possibly

different pathophysiologic syndromes with similar clinical signs resulting in an inflam-

matory skin response from exposure to an external substance.

ETIOLOGY/PATHOPHYSIOLOGY

 Differentiation between ICD and ACD may be more conceptual than practical.

 ICD: irritants directly damage keratinocytes, causing release of cytokines to induce

an inflammatory response at the lesion site:

Examples of irritants include cleansers, insecticides, plants, and chemicals (e.g.,

fertilizers, solvents)

Response depends on concentration, potency, and contact time.

 ACD: a type IV (delayed) hypersensitivity requiring sensitization and elicitation:
Sensitizers penetrate the skin, bind to carrier proteins, are processed by dendritic

cells, and lead to production of memory and effector T cells

During elicitation, memory and effector T cells damage keratinocytes (causing

cytokine release) as well as recruiting inflammatory cells to the lesion site:

Examples of sensitizers include plants, topical medications, skin care prod-

ucts, and metals

Many sensitizers are also irritants.

 There are similarities between ICD, ACD, and atopic dermatitis; epidermal barrier

defects as well as inflammation may encourage penetration of sensitizers/allergens to

produce reactions.

 The incidence of ACD is increased in atopic animals.

SIGNALMENT/HISTORY

ICD

 Occurs at any age as a direct result of the irritant nature of the offending compound.

 Reactions may occur acutely (similar to chemical burns) or after repeated exposure.

Blackwell’s Five-Minute Veterinary Consult Clinical Companion: Small Animal Dermatology, Third Edition.
Karen Helton Rhodes and Alexander H. Werner.
©2018 John Wiley & Sons, Inc. Published 2018 by John Wiley & Sons, Inc.

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