nettle rash vs efflorescence

nettle rash and efflorescence both are nouns.

Word	Noun	Adjective	Verb	Adverb
nettle rash	Yes	No	No	No
efflorescence	Yes	No	No	No

As nouns, efflorescence is a hypernym of nettle rash; that is, efflorescence is a word with a broader meaning than nettle rash:

nettle rash: an itchy skin eruption characterized by weals with pale interiors and well-defined red margins; usually the result of an allergic response to insect bites or food or drugs
efflorescence: any red eruption of the skin

Other hypernyms of nettle rash include rash, roseola, skin rash, hypersensitivity reaction.

nettle rash (noun)	efflorescence (noun)
an itchy skin eruption characterized by weals with pale interiors and well-defined red margins; usually the result of an allergic response to insect bites or food or drugs	a powdery deposit on a surface
	the time and process of budding and unfolding of blossoms
	any red eruption of the skin
	the period of greatest prosperity or productivity