There is no cellular difference between gray and white hair. These two hair colors are a result of melanin cells inside the hair follicle dying. Visually, these two colors may be caused by the amount of melanin-producing hair follicles one individual may have left.
Gray and white hair colors occur naturally as a person grows older. These pigments are not created by the presence of melanin, but instead are a result of its absence. As the human body ages, the melanin producing cells die inside the hair follicles. The strands of hair become clear or translucent once the pigment has receded. Their translucent nature, when viewed together as multiple strands by the human eye, appears gray or white in color.
Hair color is determined by the amount of pigmentation, known as melanin, present in a hair follicle. When more melanin is available, the hair follicle appears darker. Similarly, less melanin present results in a lighter color of hair. Not every hair follicle on the head of a single person will have an identical amount of melanin present, creating natural highlights in the hair of areas of darker and lighter pigmentation.
The melanin in a hair follicle may be divided into two groups: pheomelanin and eumelanin. Pheomelanin is responsible for the red shades of hair in the color spectrum. Eumelanin creates the darker brown and black colors of the hair pigment spectrum. A follicle may contain any amount of one or both of these types of melanin, lending to its overall color. Those who have lower amounts of these pigments in their hair, such as blond headed people, may find that their hair turns completely white faster than those who have high amounts of melanin and thus darker hair colors.
An individual who appears to have completely white hair is more likely to have no melanin producing cells remaining in their hair follicles. Their hair continues to grow, but it cannot produce pigmentation. Those who have gray hair, also known as a salt and pepper coloring, may have some melanin producing cells remaining. This means that some of their hair follicles have stopped creating color, but not all of them have. Those follicles that are still tinted to their hair color tend to blend in with the white strands, creating an overall grayed appearance.
The age at which this transformation occurs differs between individuals based on their genetic predispositions and their race. There is no salon product that can create gray and white hair. Salon dyes add pigment to already dead hair. The white color is only achieved once all pigmentation has been removed, and recreating this process by chemical interactions can significantly damage the hair follicles. Those who wish to speed their salt and peppered or gray and white hair to full white must wait on time to naturally complete the effect.