Our second object of study in the series is, like our first, on the outside of our bodies, that is our hair, especially hair on our heads.
First some basic facts: each hair grows out of what’s called a follicle for about three to five years, and on average, we lose 50 to 100 strands of hair a day from our heads. When a hair is shed, its follicle rests for about three months before starting to grow hair again. On average a hair grows out of its follicle at a rate of about half a millimetre per day, or about six inches (15 millimetres) per year. Given that on a full head of hair, we have about 100,000 individual hairs (although, interestingly blonds have more!), then that’s 50 metres (or yards) of total hair growth every single day, or in total over ten miles (six kilometres) of hair in a year! In fact, apart from bone marrow, hair is the fastest growing tissue in the body, with facial hair growing the fastest of all. Balding only begins to become visible once you’ve lost over half of the hairs from your head.











