Pityriasis Rosea is an erythematosquamous dermatosis. It is often misdiagnosesd as mycosis. Questioning of patients often reveals that they have worn new articles of clothing, unwashed, some days or weeks before the onset of the condition. One wonders, however, whether one would not get much the same answers from any patient questioned in the same way. Pityriasis rosea generally begins insidiously with a nummular primary lesion (primary plaque), often at the side of the trunk. The lesion may, however, occur on other parts of the body. Each has a diameter of about 1 to 5 cm, is red, scaling, with a tendency to form annuli by healing of the center with brownish discoloration (pseudoatrophy).

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The general eruption appears in crops after days or not for three or four weeks, involving chiefly the upper part of the trunk while face, hands and feet generally remain free. The red papules are round to oval and trace, in a characteristic manner, the cleavage lines of the skin. The develop fine, silvery scales. They grow paler in the center and so resemble medallions. The lesions may itch; intensive washing causes them to become edematous and infiltrated and the increased inflammation gives rise to further pruritus.

The condition is accordingly particularly intractable in patients practicing excessive body care. If the skin is left alone the condition will disappear in three to six weeks. To satisfy the patient and to save him treatment with a variety of drugs which could lead to sensitization, prescribe oil baths to be followed by application of shake lotions to the lesions.

It is necessary to exclude other exanthematous conditions by differential diagnosis, especially syphilis. Fungal infections can be mistaken for pityriasis rosea. The latter can also be simulated by dermatitis provoked by synthetic elastic fibers. A particularly difficult form of the disease to diagnose is that occurring mainly in the axilla and groin: this has been named inverse pityriasis rosea. The morphology is the same but it requires diagnostic acumen to consider it.