Why does hair always start to go grey at the temples first ?

I don't think scientists know

Extract from an article -

The process of turning gray

At the beginning of the graying process, follicles produce colorless strands in a random pattern. For unknown reasons, the first gray or white strands usually appear on your temples and the top of your head.

My first grey is a lovely silvery strand an inch back from my hair line and right on my parting :'(

When you wash your face, you inadvertently wash the temples way more than the rest of your hair.

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