genetics
Being of Irish and German decent, premature greying runs in my family. Looking at my mother and older sisters, I was not surprised that I started to get grey in my 20's.
age
From my 20's on, my hair was getting less brown and more white year after year until I went completely white by my mid to late 40's. Turning white presented an opportunity to reinvent myself...or at least mitigate the indivisibility society imposes on women of a certain age. Ahem.
drug store products
Regular use of these affordable products have given my genetically and age induced white hair, a blond (grond? bley? depending on the light, platinum?) hue. I also use heat protection spray (from the drug store) before I blow dry and flat iron.