The condition is called post-inflammatory hyperpigmentation (PIH).
This darkening of the skin is a response to to the injury or inflammation from the bite reactions. Unfortunately, as you already know, it takes a heck of a long time, i.e. two years, for complete fading. Fortunately for you, PIH is not permanent.
I would recommend you use a combination of lightening creams and superficial chemical peels at monthly intervals. You will need to use a good insecticide spray to prevent further bite reactions to get overall clear skin.
I would not recommend any light or laser based system as the heat energy can cause further heat injury to the skin and make the darkening worse. Especially on the legs. And they are expensive!
My best advice to you is that slow and steady wins the race.
Hope you found this useful.
regards,
Dr Benjamin Yim Fu Chuen
