Cause	Features
Allergic contact dermatitis	Sharply demarcated erythematous lesion with overlying vesicles
	Reaction within two to seven days of exposure (see Table 2)
Atopic dermatitis	“Itch that rashes (when scratched)” in patients with atopic conditions (e.g., allergic rhinitis, asthma)
	Involvement of flexor wrists and ankles, as well as antecubital and popliteal fossae
Bullous pemphigoid	Initially pruritic urticarial lesions, often in intertriginous areas
	Formation of tense blisters after urticaria
Cutaneous T-cell lymphoma (mycosis fungoides)	Oval eczematous patch on skin with no sun exposure (e.g., buttocks)
	Possible presentation as new eczematous dermatitis in older adults
	Possible presentation as erythroderma (exfoliative dermatitis)
Dermatitis herpetiformis	Rare vesicular dermatitis affecting lumbosacral spine, elbows, or knees
Folliculitis	Pruritus out of proportion to appearance of dermatitis
	Papules and pustules at follicular sites on chest, back, or thigh
Lichen planus	Lesions often located on the flexor wrists “6Ps”: pruritus, polygonal, planar, purple papules, and plaques
Pediculosis (lice infestation)	Occiput of school-aged children; genitalia in adults (sexually transmitted disease)
Psoriasis	Plaques on extensor extremities, low back, palms, soles, and scalp
Scabies	Burrows in hand web spaces, axillae, and genitalia
	Hyperkeratotic plaques, pruritic papules, or scales
	Face and scalp affected in children but not in adults
Sunburn teroidal	Possible photosensitizing cause (e.g., nonsteroidal anti-inflammatory drugs, cosmetics)
Xerotic eczema	Intense itching in elderly patients (often during winter months in northern climates)
	Involvement of back, flank, abdomen, waist, and distal extremities