( ( Stretch marks ) ( ( occur ( in ( ( ( the dermis ) , ) ( ( the ( middle ( skin layer ) ) ) ( which ( contains ( ( ( the ( kin 's ) ) ( elastic proteins ) ) ( that ( allowing ( the ( skin ( to ( ( ( stretch and ) return ) ( to ( its ( original shape ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Stretch) (NNS marks)) (VP (VBP occur) (PP (IN in) (NP (NP (DT the) (NNS dermis)) (, ,) (NP (NP (DT the) (JJ middle) (NN skin) (NN layer)) (SBAR (WHNP (WDT which)) (S (VP (VBZ contains) (NP (NP (NP (DT the) (NN kin) (POS 's)) (JJ elastic) (NNS proteins)) (SBAR (WHNP (WDT that)) (S (VP (VBG allowing) (NP (DT the) (NN skin) (S (VP (TO to) (VP (VB stretch) (CC and) (VB return) (PP (TO to) (NP (PRP$ its) (JJ original) (NN shape)))))))))))))))))) (. .)))
Stretch marks occur in the dermis, the middle skin layer which contains the kin's elastic proteins that allowing the skin to stretch and return to its original shape.
(ROOT (S (NP (JJS Most) (NN skin) (NNS structures)) (VP (VB originate) (PP (IN in) (NP (DT the) (NNS dermis)))) (. .)))