• Any skin disorder brought about by contact w/ an exogenous substance that triggers an allergic &/or irritant response

• Initially, lesions appear on the cutaneous site of principal exposure; may spread to other more distant sites due to contact or autosensitization
• Lesions are typically asymmetrical & unilateral
• Specific signs & symptoms will depend on the duration, location, degree of sensitivity & concentration of allergens
• Patch test shows reaction to allergen

• Acute eruptions present w/ macular erythema, papules, vesicles & bullae

• Lesions are usually lichenified, scaling, fissures w/ or without vesicles
• Pigmentary changes can occur

• Prone to irritation from chemical substances are the face, dorsum of the hands, finger webs, palms, soles or back

• Acute lesions are painful, edematous, erythematous, weepy & vesicular
• There is associated sensation of burning, stinging or pain in the site of contact to irritant
• Usually results from a single exposure to an irritant or caustic chemical

• Chronic lesions are dry, erythematous, scaling, fissuring, cracked & lichenified
• Hardening & adaptation of the skin may occur due to repeated contact w/ irritants

Common Trigger Factors

• Allergic Contact Dermatitis
  
  • Medications, certain plants, metals, foods, fragrances, stabilizers in skin products, preservatives, etc 

• Irritant Contact Dermatitis
  
  • Strong alkaline soaps, organic solvents, acid, chlorinated or bleach type ingredients, inhalants, airborne chemicals, etc

Location of inflammation may suggest trigger factors for Allergic Contact Dermatitis & Irritant Contact Dermatitis

• Eg scalp & ears
  
  • Possible trigger factors: Shampoo, hair dyes, topical medication, spectacles, metal earrings, etc

Allergic Contact Dermatitis & Irritant Contact Dermatitis may be related to occupational exposure

• Exposure to cement, epoxy, glues, paint & solvents may trigger allergic contact dermatitis
• Fuels, lubricants & cement may trigger irritant contact dermatitis