Gray Hair Growth Speed
A: No. Gray hair actually grows no faster or slower than pigmented hair does. However, when the hair turns gray it can often undergo more changes than merely color, many times changing in texture, porosity and wave pattern.
It should be noted that the decline in melanin production by the melanocytes is not typically an all or nothing proposition, since there are multiple melanocytes in a follicle and they don't usually all completely "shut down" suddenly.
As the individual melanocytes weaken and cease function (whether from genetic, environmental or medical/chemical influence) they will produce less and less melanin. This means that the hair will very gradually shift from normally pigmented to unpigmented over a significant period of time.
Where the suddenness of the transition comes in is that as the pigment is gone from the hair, the hair can shift in texture and porosity (and as a result in wave). The hair shaft will contract and become more opaque the tighter the cuticle layer becomes. These last transitions can occur more rapidly as a result of conditioning and regular hair care, which can result in the gray hair becoming more apparent in what seems like a rapid pace.
Let's face it, if the only difference was a lack of pigment, then the gray hair may not be easily noticed. Yet, if the hair is a different texture and has a different wave pattern while being different in pigment, then it is significantly more noticeable.
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See also:
Turning gray
How fast does hair grow?
Why and how hair goes gray