I had this happen to me a few times, I'm 31, they would appear during one of my active episodes of worms coming to the surface of my skin. Long gray wires hairs, all different lengths mostly around my temples.... then when the episode would get better the grey/white hairs were gone. I read this ladies blog ( Google the secrets is gratitude) she is the 3rd person to ever be diagnosed with "horsehair nematamorpha" they usually infect insects, emerging white then turning black.
I think it might be those worms and they come out in my hair cause it's dark and they can get out around the temporal bone opening. Last time this happened I used my hair straightener turned up to 450 degrees over my hair.... all the white hairs would sizzle when running the straightener over them and then they all fell out root to tip cause I had fried them. My dark normal hair was unharmed. I placed corn starch around my roots to make it dry and hard for them to retract from the heat. I know it sounds nuts but I've posted pictured of the larva coming out of my skin.