What Causes Darkening Behind Forehead?

Hi Im 58 years old.15 years back my forehead started becoming dark.My skin looks like a wrung cloth rough to touch.I ve been a very goodlooking person but due to this condition I ve stopped socializing n have become a recluse.I have visited many Doctors and one suggested that it is a genetic problem but nobody in my entire clan has had similar problem at any age.This darkening sometimes decreases and sometimes increases sp if I face the sun.Plese help me to lead a normal life.