What's the total length of hair grown on our heads in a lifetime?
An amazing 1100 kilometres - should you live to the age of 77 and avoid alopecia. An average human hair grows about 0.35 millimetres a day, and most people have between 100,000 and 150,000 hairs on their head at any one time. Most of these will fall out ater about three years to be replaced with new growth.