Most dermatologists agree that laser skin whitening is permanent however laser skin whitening doesn’t make your skin sun proof. After your surgery, you are expected to care for your skin and save it from the sun. If you don’t then there is a chance that your darken skin will return. For that reason, your dermatologist will suggest you that you use sunscreen so that your face could be safe from the sun.
The effects of laser skin whitening are usually immediate and will depend upon the type of laser used as well as the intensity of the laser. An ablative laser will show immediate results in one session however non-ablative laser will show improved effect with each session.