How do hairs go grey?
Do hairs lose their pigment and then go grey or do the coloured ones fall out and they get replaced by the grey ones?
The first thing to note is that grey hairs are not grey. They're actually white because hair colour is determined by pigment that is made by hair follicle cells. There comes a time in everyone's life where basically the pigment stops being produced. You start producing hairs that have no pigment so they're white. This mixed with your hair colour gives the grey effect. Rather than hairs starting coloured and going white, although that is possible, you tend to get hairs that start off being white.
Another question is, does people's hair really go grey overnight?
Kat: I have looked at it a bit and there seems to be a bit of an argument in it. The only way I can see it's possible is if someone has very short hair. They go grey due to some stress event. Maybe their hair's falling out. It might look like over a very short period of time if you have very short hair that you're going grey overnight.
Chris: I've seen patients who have a hair which they've showed me themselves and say, "This is interesting doc, look at this." It's white at the base and then brown halfway along because it's literally run out of melanin to add to the hair and it's changed colour.