The medical term for stretch marks is Striae distensae, and exact causes for it are still unknown. Some researchers think they are caused by the overstretching of connective tissue in the skin or by hormones. Others theorize they run in the family or can even be caused by a type of infection.
No matter the cause, about 68% of women and 24% of men develop stretch marks.
A number of events and conditions can cause stretch marks.


As many as 90% of women get stretch marks when they are pregnant. It's not surprising that these marks commonly occur first during the sixth and seventh months - when the body is changing to prepare for delivery and the baby is large enough that the mother can feel her baby's body or head when she touches her stomach. During this time, stretch marks can appear on the stomach, hips and breasts.


The way skin reacts to weight change also causes stretch marks. People who gain weight quickly can develop stretch marks, and losing weight quickly after gaining weight might even make stretch marks more noticeable because the skin becomes looser and less taut.


Growth or stretching of skin over a short period of time can also cause stretch marks. This is why they are common in adolescents during growth spurts. During these periods of rapid growth, stretch marks commonly occur in boys on the outer thighs and lower back. In girls, the marks are more common in the thighs, upper arms, buttocks and breasts. About 70% of adolescent girls and 40% of adolescent boys have stretch marks.


Though stretch marks are caused most often by pregnancy and rapid growth or changes in weight, other conditions can cause them as well:

  • Some types of bodybuilding where muscle mass increases quickly.
  • Stretching skin at the site of stitches.
  • Overuse of steroids, cortisone skin creams or corticosteroids (Cushing syndrome).
  • Some inherited conditions that affect connective tissues (Ehlers-Danlos syndrome).