noun, noun which may take the genitive case particle 'no'
Anatomical term for the pigmented circular area surrounding the nipple.
乳輪の大きさや色には個人差がある。
The size and color of the areola vary from person to person.
乳首 refers specifically to the nipple itself, while 乳輪 refers to the surrounding areola.
From 乳 (にゅう, 'milk, breast') + 輪 (りん, 'ring, circle'), referring to the circular area around the nipple.