dandruff vs pityriasis

dandruff and pityriasis both are nouns.

Word	Noun	Adjective	Verb	Adverb
dandruff	Yes	No	No	No
pityriasis	Yes	No	No	No

As nouns, pityriasis is a hypernym of dandruff; that is, pityriasis is a word with a broader meaning than dandruff:

dandruff: a condition in which white scales of dead skin are shed by the scalp
pityriasis: any of several skin disorders characterized by shedding dry flakes of skin

dandruff (noun)	pityriasis (noun)
loose scales shed from the scalp	any of several skin disorders characterized by shedding dry flakes of skin
a condition in which white scales of dead skin are shed by the scalp