pityriasis

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pityriasis (pit-i-ry-ă-sis) n. (originally) any of a group of skin diseases typified by the development of fine branlike scales. p. alba a common condition in children in which pale scaly patches occur on the face. p. capitis see dandruff. p. rosea a common skin rash, believed to be viral in origin, that starts with a single patch on the trunk and is followed by an eruption of oval pink scaly macules. The rash clears completely in about eight weeks. p. versicolor a common chronic infection of the skin caused by the fungus Pityrosporum orbiculare, a normal inhabitant of the scalp that in susceptible people changes to a pathogenic form on the trunk.