Anything from weight gain to weight loss can cause that, my brother wanted to build muscle so he started working out, and as the muscle started like showing his skin started to stretch to accomodate the muscles and he started having stretch marks like on his shoulders.
a bit wrong. is nt about weight loss. stretch marks appear wen ur skin stretches i.e wen ur bcomin bigger or mo fat. also dey very often appear wen ur a teenager cuz teenagers grow very fast n skin dsnt hav tym 2stretch normally. beside if ur skin is in gud condition n ur takin care of it + ur fit den u wil neva hav stretch marks afta child birth