How long does it take for lightener to work?

A lightening agent (for dark spots) like hydroquinone, mulberry, licorice, or kojic acid can begin to work in days, but it usually takes weeks to see an appreciable reduction in pigment. If you see no difference in three or four weeks, it's probably not going to work.

Is lightener bad for your hair?

It's no secret that bleaching your hair can damage it, but that doesn't mean you shouldn't do it! ... You have probably heard that bleaching and highlighting your hair can damage it. This is true, bleaching agents are hard on your strands. They can make your hair dry, brittle, frizzy-looking and prone to breakage.