Stretch marks form when skin is stretched faster than it can adapt, tearing the collagen and elastin in the dermis. Growth spurts, pregnancy, rapid weight change and bodybuilding all do it, and genetics decides how prone you are more than anything you could have done differently.
The single most useful thing to know is that they change over time, and that treatment works far better in the first phase.
Fresh stretch marks are red or purple, which means there is still blood supply and active inflammation in the tissue. That is a live wound and it responds to treatment.
Mature stretch marks are white or silver, sometimes slightly indented. The inflammation has resolved, the vessels have gone, and what remains is essentially scar tissue with no pigment cells. These improve with treatment, softening in texture and fading in visibility across a course.
Regents Park Aesthetics treats stretch marks at the Wimpole Street clinic, a short walk from Oxford Circus. Your clinician tells you which phase yours are in and exactly what you can look forward to.