Table 1.

Differential diagnosis between allergic contact dermatitis (ACD) and irritant contact dermatitis (ICD).

Criteria	ACD	ICD
Occurrence	Skin lesions develop usually 5–7 days after first contact with allergen or 24–48 h after a further contact	Skin lesions appear few hours after first contact with substance
Symptoms	Itch, usually strong	Burning, rarely itch
Limits of lesions	Blurred. They tend to overcome the area of contact with allergen	Well defined, they often trace the shape of the irritant product and are limited to the contact area
Morphology	Acute eczema (erythema, oedema, vescicles) or dry eczema (erythema and desquamation)	Erythema and desquamation
Idic eruptions	May be present	None
Skin test	Positive patch test for culprit allergen	None
Histopathology	Spongiform dermatitis	Necrosis, acantolysis, intraepidermical bullae due to caustic damage to epidermis