why does my a** have stretch marks?

Fastest way to remove stretch marks is to manually scrub them off not to apply creams. I used special scrub with medical crystals (these crystals are round and super hard so they never melt or injure skin if you rub too hard)

So I massaged this medical crystals rub for stretch marks in circles while taking shower and after I rinse I apply stretch mark oil (organic Green15 oil for stretch marks) All my smaller stretch marks are gone within 1 month, still need to work on bigger ones but they did fade.

Have you had a baby? My privates have stretch marks from pushing kids out. Weight can be a factor in giving stretch marks too. Unfortunately, stretch marks will be with you through-out life. You can 'lighten' them with lotions.