A stretch mark (or sometimes known as Striae) is a type of scar that develops when our skin stretches or shrinks quickly such as pregnancy, rapid weight gain, muscle expansion from weights training or during puberty. This rapid skin stretch causes the skin’s supporting collagen and elastin fibres to rupture. As the skin heals, new irregular collagen and blood vessels fill that stretched area and stretch marks which often appear red may appear. It takes months and sometimes years for these striae to die down in colour.