Chapter 2. Contact Dermatitis
Contact dermatitis refers to a group of common eczematous conditions in which an inflammatory reaction in the skin is triggered by direct contact with an environmental agent. This section covers the two major forms of contact dermatitis and an approach to management :
Irritant contact dermatitis is the most common type (representing 80% of contact dermatitis) and results from a direct cytotoxic effect on the skin from an irritant chemical agent. With irritant contact dermatitis, any individual with long enough exposure to the irritant will eventually develop a reaction. The rash usually occurs within minutes, is pruritic, and consists of erythema, edema, vesicles and crusts. Common irritants include acids, alkalis, and hydrocarbons. Patients with atopic dermatitis are more predisposed to develop irritant contact dermatitis because of the disturbed barrier function of the skin.
Irritant dermatitis can occur for a number of reasons and in different locations on the body. In infants, a rash can form around the mouth secondary to chronic occlusion of saliva by a pacifier against the facial skin. This type of dermatitis is generally eczematous in morphology with fine, red scale to the perioral area often involving the vermillion border (PICTURE A). It is treated with thick emollients and behavior modification when appropriate. Likewise, "lip-licker’s" dermatitis is an irritant contact dermatitis resulting from the chronic wet-to-dry cycle caused by lip-licking (PICTURE B). Irritant dermatitis may also be seen in adults, especially those whose occupations or personal behaviors cause them to overwash their hands (PICTURE C).
Allergic contact dermatitis is a type IV, delayed-type hypersensitivity reaction that occurs when the skin comes in contact with a chemical (antigen) to which the individual is already sensitized. Initial sensitization takes days to weeks but repeat exposures cause a more rapid reaction occurring within hours to days. (PICTURE A) The acute rash is identical in morphology to that of irritant contact dermatitis; however, the rash of allergic contact dermatitis may also become chronic, depending on how quickly the inciting agent is identified. In chronic cases, findings are similar to those of chronic atopic dermatitis: lichenification, scaling and pigmentary changes. Common contact allergens include plants (poison ivy, oak and sumac), nickel, rubber, glues, dyes (often in shoes), and other chemicals found in clothing. Neomycin (topical antibiotic) is also a common sensitizer. Protein contact dermatitis is commonly seen in children; common inciting agents include latex, insects, and food substances.
Rhus dermatitis (poison ivy, poison oak, poison sumac) is the most common allergic contact dermatitis in the United States. The rash consists of linear streaks of erythematous papules and vesicles (PICTURE B) that appear where the plant has brushed against the skin. Impressive edema is sometimes seen, particularly when the face or genitals are involved (PICTURE C). The dermatitis is produced by both direct contact with the poison sap and by indirect contact (such as with an animal or clothing that has had contact with the plant). The rash is not spread by the fluid contained within the vesicles. Antigen retained on the skin may initiate new lesions, but once on the skin for about 20 minutes, the allergen becomes fixed and cannot spread further. Thorough washing of the skin after a known exposure may decrease the amount of remaining sap and therefore reduce the severity of the eruption. Additionally, barrier creams applied prior to exposure may be protective.
In both irritant and allergic contact dermatitis, history of an inciting agent helps to make the diagnosis; consequently, removal of the agent should result in clearing of the dermatitis. In difficult cases, patients may be referred to a specialist for patch testing in an attempt to isolate the allergen. Mid-potency topical corticosteroids are generally used to control pruritis and hasten healing for lesions not involving the face, axilla or groin. In these areas, low-potency preparations, such as 1% hydrocortisone cream, or topical calcineurin inhibitors (Elidel or Protopic) should be used. Oral corticosteroids are indicated for treatment of severe cases. When used, oral corticosteroids should be taken for approximately one week and then tapered over 1-2 additional weeks to prevent rebound flaring of the dermatitis.