What Causes Pigmentation On The Forehead?

Dear sir/madam,
My self an 'Ex-Professsor of Electrical Engg., Banaras Hindu University';presently after retirement,
staying with my son`s family in greenpark.
About 18 months back, I discovered DARKENED-skin on left-side of 'my Forehead',starting from hair-line
downwards up to left-eyebrow. Since then, I have been using 'ayuvedic-rakta shodhak orally',and Himalaya -
night cream/Vico`s skin cream,topically; for some time.
It looked controlled ;though slightly faded, it spread to right side of theForehead also. Presently, I am taking
'Homeopathic blood purifier Regleck-medicine', and some sun-screen-lotion.

It looks like fading, but I am NOT SURE OF SYSTEMATIC REDUCTION.
Above description is the 'HISTORY OF MY CASE' .
Thanking you,
Dr.NAGARAJ T(Rtd.Professor)