Do skin diseases characteristically occur in certain locations?

Yes. This is the reason that a complete skin examination should be performed on all patients. Seborrheic dermatitis characteristically occurs on the scalp, nasolabial folds, retroauricular areas, eyelids, eyebrows, and presternal areas; it tends to spare the extremities. Psoriasis may resemble seborrheic dermatitis, but it characteristically demonstrates a different distribution, usually involving the extremities (elbows, knees), intergluteal fold, scalp, and nails.