The visibility of stretch marks does not depend solely on the stretching of the skin itself, but primarily on its biological structure. In some people, collagen and elastin fibres are naturally weaker or less organised, which is due to genetic factors. This means that the skin is less able to cope with sudden changes in tissue volume. Hormonal differences also play a role – particularly levels of oestrogen and cortisol, which influence the skin’s repair processes. In people with a predisposition, stretch marks may be deeper, wider and more permanent even at an early stage. Furthermore, the thickness of the skin in different parts of the body plays a significant role – for example, the skin on the abdomen and thighs is more susceptible to damage than the skin on the back. As a result, in some patients, the stretch marks are more visible and more difficult to treat without therapies that stimulate collagen remodelling.