Acne vulgaris | Face, upper back, chest | Open and closed comedones, erythematous papules, pustules, cysts | Seborrheic keratosis | Trunk, face, extremities | Brown plaques with adherent, greasy scale; “stuck on” appearance |
Rosacea | Blush area of cheeks, nose, forehead, chin | Erythema, telangiectases, papules, pustules | Folliculitis Impetigo | Any hair-bearing area Anywhere | Follicular pustules Papules, vesicles, pustules, often with honey-colored crusts |
Seborrheic dermatitis | Scalp, eyebrows, perinasal areas | Erythema with greasy yellow-brown scale | Herpes simplex | Lips, genitalia | Grouped vesicles progressing to crusted erosions |
Atopic dermatitis | Antecubital and popliteal fossae; may be widespread | Patches and plaques of erythema, scaling, and lichenification; pruritus | Herpes zoster | Dermatomal, usually trunk but may be anywhere | Vesicles limited to a dermatome (often painful) |
Stasis dermatitis | Ankles, lower legs over medial malleoli | Patches of erythema and scaling on background of hyperpigmentation associated with signs of venous insufficiency | Varicella | Face, trunk, relative sparing of extremities | Lesions arise in crops and quickly progress from erythematous macules, to papules, to vesicles, to pustules, to crusted sites. |
Dyshidrotic eczema | Palms, soles, sides of fingers and toes | Deep vesicles | Pityriasis rosea | Trunk (Christmas tree pattern); herald patch followed by multiple smaller lesions | Symmetric erythematous papules and plaques with a collarette of scale |
Allergic contact dermatitis | Anywhere | Localized erythema, vesicles, scale, and pruritus (e.g., fingers, earlobes—nickel; dorsal aspect of foot—shoe; exposed surfaces—poison ivy) | Tinea versicolor | Chest, back, abdomen, proximal extremities | Scaly hyper- or hypopigmented macules |
Psoriasis | Elbows, knees, scalp, lower back, fingernails (may be generalized) | Papules and plaques covered with silvery scale; nails have pits | Candidiasis | Groin, beneath breasts, vagina, oral cavity | Erythematous macerated areas with satellite pustules; white, friable patches on mucous membranes |
Lichen planus | Wrists, ankles, mouth (may be widespread) | Violaceous flat-topped papules and plaques | Dermatophytosis | Feet, groin, beard, or scalp | Varies with site (e.g., tinea corporis—scaly annular plaque) |
Keratosis pilaris | Extensor surfaces of arms and thighs, buttocks | Keratotic follicular papules with surrounding erythema | Scabies | Groin, axillae, between fingers and toes, beneath breasts | Excoriated papules, burrows, pruritus |
Melasma | Forehead, cheeks, temples, upper lip | Tan to brown patches | Insect bites | Anywhere | Erythematous papules with central puncta |
Vitiligo | Periorificial, trunk, extensor surfaces of extremities, flexor wrists, axillae | Chalk-white macules | Cherry angioma Keloid Dermatofibroma | Trunk | Red, blood-filled papules |
Anywhere (site of previous injury) | Firm tumor, pink, purple, or brown |
Anywhere | Firm red to brown nodule that shows dimpling of overlying skin with lateral compression |
Actinic keratosis | Sun-exposed areas | Skin-colored or red-brown macule or papule with dry, rough, adherent scale | Acrochordons (skin tags) | Groin, axilla, neck | Fleshy papules |
Basal cell carcinoma | Face | Papule with pearly, telangiectatic border on sun-damaged skin | Urticaria | Anywhere | Wheals, sometimes with surrounding flare; pruritus |
Squamous cell carcinoma | Face, especially lower lip, ears | Indurated and possibly hyperkeratotic lesions often showing ulceration and/or crusting | Transient acantholytic dermatosis | Trunk, especially anterior chest | Erythematous papules |
Xerosis | Extensor extremities, especially legs | Dry, erythematous, scaling patches; pruritus |