Could be diet (a lack of fat) and/or genetic.
Either way, once you have them they can't be cured. They fade and if you have pleny of money you can go to doctor to let him cut damaged skin.
You could buy some creme's to prevent getting worse but don't spend your money on the extensive ones. The do nut really help. There are some people who claim the massaging effects of rubbing creme (oil) on the area helps the bloodflow in the lower skin. You should give it a try, sounds reasonable.