why does hair change colour and turn grey?

What determines the colour of hair?

Most of us find our first “greys” by the time we turn 30, usually at the temples, then later, across the scalp. While many people find the salt and pepper look appealing, others go to great lengths to conceal these locks.

The grey hair “rule of thumb” is that by the age of 50, half of the population have lost the colour in 50% of their hair. When researchers tested this rule, they found that 74% of people aged between 45 and 65 had grey hair, with an average intensity of 27%.

Generally, men have more grey hair than women. Asians and Africans have less grey hair than Caucasians./.../