noun, noun which may take the genitive case particle 'no'
too thin; underweight
Describes a person or body that is excessively thin, often with a negative or health-related connotation. Can be used as a noun or with の to modify another noun.
彼女は痩せすぎで、健康が心配だ。
She is too thin, and I'm worried about her health.
痩せすぎのモデルが問題になっている。
Underweight models have become a problem.
痩せる is the verb 'to lose weight' or 'to be thin'; 痩せすぎ is the noun/adjective meaning 'too thin' or 'underweight'.
Compound of 痩せ (continuative form of 痩せる, 'to lose weight') + すぎ (from 過ぎる, 'to exceed').