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INTRODUCTION TO CHAPTER

Dermatitis (eczema) refers to a heterogeneous group of inflammatory skin disorders that share similarities in clinical appearance and histopathologic findings but may have very different etiologies. It is a common disorder, affecting 1 in 5 people at some point in life. Dermatitis may be acute, subacute, or chronic. In its acute stage, dermatitis is marked by erythema, edema, and vesicles, while chronic dermatitis is characterized by lichenification, fissures, and scaling. Dermatitis can further be delineated as either endogenous (internal factors) or exogenous (external factors). Pruritus is a common symptom of all types of dermatitis.

CONTACT DERMATITIS

Contact dermatitis is an exogenous form of dermatitis divided into two major categories: Irritant contact dermatitis and allergic contact dermatitis (Table 8-1). Irritant contact dermatitis is more common (80% of cases) than allergic contact dermatitis (20%); however, these reactions are not mutually exclusive and may occur simultaneously in a particular patient. For example, contact allergy to a glove chemical may complicate irritant hand dermatitis due to irritating soaps used for hand washing. Furthermore, one product may act as both an irritant and allergen; a patient may have an allergic reaction to a preservative in a liquid soap as well as having an irritant reaction to a detergent in the soap. Common irritants include water, soap, industrial cleansers, and frictional forces; additional irritants are listed in Table 8-2. Common allergens are listed in Table 8-3.

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Table 8-1. Comparison of irritant contact dermatitis and allergic contact dermatitis.
  Irritant contact dermatitis Allergic contact dermatitis.
Onset

Strong irritants – Within minutes.

Weak irritants – Days to weeks.

Within 24–96 hours in sensitized individuals.
Resolution May improve within days after exposure, some cases may persist. Improves after 3–6 weeks away from exposure.
Mechanism Nonimmune, sensitization not required; epidermal barrier disruption, epidermal cellular damage, pro-inflammatory mediators released from keratinocytes. Immune-mediated, sensitization required. Antigen activated primed T-cells; sensitization phase typically takes 10–14 days but can occur immediately or after years.
Agent Concentration dependent. Not concentration dependent.
Diagnosis Clinical. Patch testing.

Table 8-2.Examples of common skin irritants and their sources.
Table 8-3.Common allergens.

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