An age-old hair myth is that hair can turn grey or white overnight. Scientifically, it is impossible for your hair to turn grey or white overnight. The hair that you see on your head has its colour genetically formed. Hair colour can only be changed by applying a bleach or colouring agent. Therefore, unless someone has snuck into your room at night and treated you to a set of highlights, you cannot wake up one morning to find all of your existing hairs have turned grey or white overnight.
‘My hair has gone grey / white overnight’ is also one of those dramatic statements used to convey the degree of stress somebody has undergone. Stress can in fact affect hair colour and cause it to turn grey or white, but this happens gradually and as the hair is growing. A huge shock to your body or system can also cause hair to turn grey or white more rapidly. It is thought that both stress and shock interfere with the production of melanocytes,which make melanin, the pigment granules which give hair its colour. However, unless you are Rip Van Winkle, it is impossible for this to happen overnight.
That said, all myths must come from somewhere and have an underlying element of truth or plausibility. The hair turning grey or white overnight myth is probably linked to alopecia areata . Alopecia areata causes clumps of hair to fall out and these fallen hairs are replaced initially with white hairs or, more accurately, unpigmented hairs. However, even this change in your hair can’t occur overnight.