I dye mine every 6 weeks or so. I go to a ladies hair salon and use the same dye and color service that women use. It is by far the best way to cover grey, and get the longest lasting coverage. They've been doing it for eons, take advantage of what they have learned!
I used to use over the counter dyes that you can buy at the drug store "just for men" and the dyes that the leading manufacturers sell. ( clairol, etc..)
But, they just don't cut it as far as grey coverage is concerned. You wind up looking like you've used shoe polish on your head...AND , you can wind up dying your skin in the process.
I've found that coloring, with a bit of highlighting does the trick quite well. And, spending an hour or two with a good looking woman coloring, cutting, and shampooing my hair is a good thing indeed.
As far as the non-toxic issue goes, i'm not sure.
Personally, I wouldn't think twice about it...
Better to have a head of grey hair to color, than a smattering of stubble to shave off..
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victory begins with a mindset...