mastitis vs redness

mastitis and redness both are nouns.

Word	Noun	Adjective	Verb	Adverb
mastitis	Yes	No	No	No
redness	Yes	No	No	No

As nouns, redness is a hypernym of mastitis; that is, redness is a word with a broader meaning than mastitis:

mastitis: inflammation of a breast (or udder)
redness: a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat

Other hypernyms of mastitis include inflammation, rubor.

mastitis (noun)	redness (noun)
inflammation of a breast (or udder)	red color or pigment; the chromatic color resembling the hue of blood
	a response of body tissues to injury or irritation; characterized by pain and swelling and redness and heat