Definition: Pityriasis is any
of several skin disorders, including dandruff.
Pityriasis alba, Common skin
disorder, occuring most often in children and young adults,
characterized by circumscribed round or oval patches of depigmentation
(loss of normal pigment), or less than normal pigmentation.
Pityriasis rosea, skin disease
in which a mildly itchy rash develops over the trunk of the
body several days after a single localized patch called a
Pityriasis rubra pilaris refers
to a group of chronic disorders characterized by reddish orange,
scaling plaques and keratotic follicular papules. Also known
as "Devergie's disease," "Lichen
ruber acuminatus," and "Lichen ruber pilaris".
Pityriasis rubra pilaris outbreak
on the arm
Severe case of Pityriasis rubra pilaris
Notes from Medical Textbook about image
above: "Pityriasis rubra pilaris in a mulatto
girl, involving the entire surface. Began when six or seven
years old, and gradually extended, reaching generalization
when ten years old (at the time this photograph was taken).
Family free from skin disease, and brothers and sisters, six
in all, when last seen, then aged 16, not more than one-third
of the surface remained affected, the eruption then consisting
of some large confluent scaly areas and patches of closely
crowded discrete follicular papules. The patient's general
health has continued good throughout."
Above and below, Pityriasis rubra
pilaris as it appears under an early 20th Century microscope.