Contact dermatitis presents as either allergic or irritant in etiology. While irritant contact dermatitis represents the direct toxic effect of an offending agent on the skin, allergic contact dermatitis (ACD) represents a delayed-type (type IV) hypersensitivity reaction that occurs when allergens activate antigen-specific T cells in a sensitized individual. Consequently, whereas irritant contact dermatitis can occur after one exposure to the offending agent, ACD typically requires repeat exposures before an allergic response is noted. ACD can occur 24-48 hours after exposure to the offending agent.
ACD can occur in response to topical agents, systemic exposure via ingestion, or innocuous transfer of the culprit agent via the fingertips.
Use of soap, topical anesthetic agents, spermicides, rubber accelerators found in condoms, and topical steroids have all been reported to cause ACD in the genital area. Lipstick-induced penile dermatitis has not been reported but is noted as a theoretical concern for men sensitive to octyl gallate.
Passive transfer of poison ivy resin has been implicated in penile ACD.
ICD10CM: L23.9 – Allergic contact dermatitis, unspecified cause
SNOMEDCT: 40275004 – Contact dermatitis
Differential Diagnosis & Pitfalls
Cellulitis – Plaque margins in cellulitis are often less distinct than those of contact dermatitis. The plaques of contact dermatitis are sharply demarcated and frequently take on bizarre geometric shapes and patterns.
Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.
Allergic contact dermatitis is a delayed hypersensitivity reaction (the reaction to the allergen occurs 48–72 hours after exposure). The most common allergens causing allergic contact dermatitis often change with time, as certain chemicals come in or out of use in the manufacture of products that come in contact with the skin. Most recently, common causes of allergic contact dermatitis include nickel, chromates, rubber chemicals, and topical antibiotic ointments and creams. Frequent sensitizers in the general population also include fragrance, formaldehyde, lanolin (wool grease found in ointments and cosmetics), and a host of other common environmental chemicals.
Nickel is found in jewelry, belt buckles, metal closures on clothing, and some cell phones.
Chromates are used in the process of tanning leather for shoes and in cement, so they can affect construction workers who are in contact with cement.
Rubber chemicals are found in gloves, balloons, elastic in garments, mouse pads, and swim goggles.
Neomycin is common in triple antibiotic first aid ointments such as Neosporin (and generic versions of Neosporin) as well as other combination preparations with other antibacterials (eg, Polysporin). It may also be found in eye preparations and eardrops. Bacitracin is a common ingredient in antibiotic ointments and creams and can cause allergic contact dermatitis as well.
Common allergen-containing products include sunscreens (oxybenzone [benzophenone-3]), cosmetics, soaps, dyes, and jewelry.
Poison ivy is a frequent cause and is discussed separately.
Who’s At Risk
Allergic contact dermatitis can occur at any age in people of all ethnic backgrounds. Individuals with a skin condition (such as stasis dermatitis, otitis externa, or pruritus ani) requiring frequent application of topical agents can develop allergic contact dermatitis over time.
Signs & Symptoms
Allergic contact dermatitis may occur on any location of the body.
Scaly red to pink areas of elevated skin (papules and plaques) and blisters (vesicles) may be seen. Individual lesions have distinct borders and often have a geometric shape with straight edges and sharp angles.
Eyelid swelling is frequently seen when the allergen is unknowingly transferred from finger to lid. Affected areas are typically severely itchy.
When the dermatitis is long-standing, the areas of elevation become thick and secondary bacterial infection is possible.
Avoid the offending agent.
It may be helpful to avoid common triggers, such as fragrance, lanolin, nickel, etc.
1% over-the-counter hydrocortisone cream can be helpful in very mild cases. Topical (applied to the skin) antihistamines should be avoided.
When to Seek Medical Care
Seek medical evaluation for a persistent or recurrent rash of unknown origin. Your physician may perform patch testing to evaluate for potential contact allergies. Skin biopsy is sometimes used to confirm diagnosis.
Treatment is aimed at preventing contact with the allergen.
Symptomatic control of itching may include oral antihistamines.
Medium- and high-potency topical steroids may be prescribed for rashes occurring on the extremities or trunk.
Mild-potency topical steroids may be prescribed for thinner skin on the face and skin fold areas.
In severe cases involving large body areas, a course of an oral steroid (prednisone) may be prescribed.
Bolognia, Jean L., ed. Dermatology, pp.227, 252-256. New York: Mosby, 2003.