Dr. King recommends starting to use a stretch mark cream before you have them, treating them as more of a preventative measure. So, if you’re expecting or plan to be soon, get into the habit of applying a stretch mark cream daily. However, if you’re looking to improve the appearance of existing stretch marks and don't plan to visit your dermatologist for an in-office treatment, it’s best to start using a stretch mark cream as soon as you see it form for best results.