The eruption makes its appearance, as a rule, somewhat rapidly, usually attaining its full development in the course of one or two weeks, and then begins gradually to decline, the whole process occupying one or two months. #To what is pityriasis rosea to be attributed?# The cause is not known; it is variously considered as allied to seborrh[oe]a (eczema seborrhoicum), as being of a vegetable-parasitic origin, and as a mildly inflammatory affection somewhat similar to psoriasis. It is not a frequent disease. #How is pityriasis rosea distinguished from ringworm, psoriasis and the squamous syphiloderm?# From ringworm, by its rapid appearance, its distribution, the number of patches, and, if necessary, by microscopic examination of the scrapings. Psoriasis is a more inflammatory disease, is seen usually more abundantly upon the limbs, the scales are profuse and silvery, and the underlying skin is red and has a glazed look; moreover, psoriasis, as a rule, appears slowly and runs a chronic course. The squamous syphiloderm differs in its history, distribution, and above all, by the presence of concomitant symptoms of syphilis, such as glandular enlargement, sore throat, mucous patches, rheumatic pains, and falling out of the hair. #State the prognosis of pityriasis rosea.# It is favorable, the disease tending to spontaneous disappearance, usually in the course of several weeks or one or two months. #What treatment is to be advised in pityriasis rosea?# Laxatives and intestinal antiseptics, and ointments of salicylic acid (5-15 grains to the ounce), of sulphur (10-40 grains to the ounce); or a compound ointment containing both these ingredients can be prescribed. The ointment base can be equal parts of white vaselin and cold cream; in some instances Lassar's paste (starch powder, zinc oxid powder, each, [dram]ij; vaselin, [dram]iv) seems more satisfactory. #Dermatitis Exfoliativa.# (_Synonyms:_ General Exfoliative Dermatitis; Recurrent Exfoliative Dermatitis; Desquamative Scarlatiniform Erythema; Acute General Dermatitis; Recurrent Exfoliative Erythema; Pityriasis Rubra.) #Describe dermatitis exfoliativa.#