What Causes Appearance Of Dark Red Indented Lines On Inner Thighs And Left Armpit?

Hey, i ve recently noticed dark red indented lines on inner thighs, and left armpit. i haven t lost gained weight and am not taking any meds. I m also fairly fit and kept my weight down and haven t had any recent illnesses. i m 21 and never had any stretch marks. the one on my armpit i ve had since i first had heart problems, but the other ones are new and slowly getting more prominent