Striae gravidarum (stretch marks developing during pregnancy) occur in 50% to 90% of women. They appear as red or purple lines or streaks that fade slowly to leave pale lines or marks on the skin. The abdomen, breasts and thighs are commonly affected. The exact cause of stretch marks is unclear and no preparation has yet been shown to be effective in preventing the development of stretch marks. They are a source of significant anxiety for women, impacting on their quality of life.