Melgain Lotion is used in the treatment of vitiligo. How to use: This medicine is for external use only. Use this medicine in the dose and duration as advised by your doctor. Shake it well and apply to the area evenly. How it works: Melgain Lotion is a regimenting agent. It works by causing migration of skin cells (melanocytes) from the area of skin surrounding the vitiligo patch. This in turn causes the production of melanin (skin darkening pigment) and restores the skin colour.