Red lines/Scratch marks

I am 16 years old (a bit on the chubby side) and in the past few weeks i have realized light red coloured lines under my arm pits and on the side of my hip (both sides) . The lines aren't long but look like small scratches. Any insight is appreciated.

[jagesh50]

These are striae and as to why the come to some remains sort of a mystery,of course puberty,and obesity well known associations.May be you can apply aloe vera creme.