Gray Hair Growth after Dyeing

Hair with gray roots
Q: I am a 54 year old woman with dyed hair. My original hair is dark brown with salt & pepper coloring at the top of my head. I've noticed more hair loss than normal after having dyed my hair lately with burning scalp reactions.
So I stopped dyeing my hair for six weeks and noticed all the new hair growth is all gray at the top of my head. I had been highlighting my hair with lighter colors also. And I have found that the growth of the highlighted tinted lighter hair, at the top of my head, remains dark at the roots.
Question 1: Why hasn't these highlighted hairs turned gray at the roots, even though the hair has grown out?
Question 2: And why has only the new hair turned gray; there are no new dark brown hairs anywhere on my head, even in the natural dark area of my head?

A: The process which turns hair gray naturally as we age is genetic, although aging isn't the only cause of gray hair (technically referred to as canities). Stress, injury or prolonged illness can also cause graying of the hair.
You've mentioned that you experienced hair loss and a burning scalp after recent hair dyeing processes. What it sounds like is that the chemical burns you sustained (which were obviously serious enough to result in hair loss) damaged the hair follicle and have resulted in new hair growth with loss of pigment. This also explains why the "new growth" of the hair that wasn't lost has remained dark.
Another thing to bear in mind is that we are used to thinking of our hair as a whole, when each follicle operates and acts independently. Each follicle grows at its own pace, reacts independently, and can be sensitive to (or resistant to) chemicals, regardless of the others' reactions.
The likely cause of the situation you describe is that the hair follicles which were sensitive to the chemicals reacted by shedding the hair and the stress of the burn caused them to produce new hair growth that was without pigment. The rest of your hair follicles were less sensitive and therefore didn't react to the chemical burn.
Photo: Evg Zhul/Shutterstock
See also:
Hair loss
How hair turns gray
Hair color allergies
Will coloring damage my hair?