Recently, researchers at New York University Grossman’s school suggested in their findings of how hair gets pigmented.
They stated that melanin which is the natural colour pigment in the skin and hair shaft is produced by cells called melanocytes and the stem cells that produce these move cyclically from the area near the sebaceous gland to the root of the hair where the process then begins of incorporation of melanin into the hair shaft as it develops.
This process is genetically determined and when people go grey with age, the hair shaft doesn’t get pigmented (although this has occurred in very rare cases).
More importantly, in the over 80 year old age group, if some of the hair strands turn back to colour from grey, there may be a sinister cause. Two studies published in 2019 and 2022 gave examples of 2 cases of men in their mid 80s whose hair underwent depigmentation to brown/black. On investigating, it was discovered that the cause was lentigo maligna which is a variant of melanoma that occurs in sun damaged scalp.
Therefore, if cases of depigmentation occur, the health professional and the patient needs to be aware that this may be a sign of lentigo maligna.