Acne vulgaris: comedones, papules, pustules, and nodules, occasionally with scars, on the face, neck, chest, and back. Concomitant hyperandrogenism may occur in women with acne, hirsutism, and irregular menses.

Rosacea: erythema, telangiectasia, papules, and pustules.

Seborrheic dermatitis: erythematous plaques with greasy, yellow scale. Common and extensive in adults with neurologic disorders such as Parkinson’s disease and human immunodeficiency virus infection.

Seborrheic keratoses: warty, age-related plaques. May indicate an underlying adenocarcinoma of the gastrointestinal tract.

Urticaria: pruritic, edematous, evanescent wheals that usually resolve within 24 hours.

Pruritus: aquagenic pruritus is unique to polycythemia vera.

Drug eruptions: occur in approximately 2% of all hospitalized patients.

Erythema multiforme: the most common cause is recurrent herpes simplex virus infection; less common: Mycoplasma pneumonia and medications.

Psoriasis: silvery-white scaly papules and plaques commonly on the scalp, elbows, and knees, and/or nail dystrophy. Patients are at an increased risk for the metabolic syndrome.

Vitiligo: depigmented macules. Some patients have an associated autoimmune disease.

Erythema nodosum: painful reddened nodules on the shins, thighs, or forearms. Common causes: streptococcal pharyngitis, drugs, illnesses (inflammatory bowel disease, sarcoidosis).

Pemphigus vulgaris: painful mucosal erosions and flaccid eroded blisters. Immunoglobulin (Ig)G deposits within the epidermis. Even with treatment, associated with a high morbidity and mortality.