Kayla Adams, of Palmerston North, asks :-

Why does hair colour change with age?

Peter Dearden, a geneticist at the University of Otago's Biochemistry Department, responded.

As we develop from embryos to babies our genes, the “recipe” that makes us each unique and different, directs the formation of our cells and tissues. Our genes tell our bodies what colour hair we will have, what colour eyes, if we will be short or tall, or if we will have dad’s nose or mum’s ears. Most of what makes you YOU come from your genes.

In dark-haired people your hair colour is set before you are born and does not change until you are old and your hair goes white or grey, or sometimes even falls out all together. We know why hair goes white with age. It is the cells that make the pigment (the chemicals in your skin and hair that make it’s colour) slowly dying as you age and no longer producing enough pigment to keep your hair its original colour. This is a normal part of aging. The cells that make pigment (called melanocytes) are born when you are an embryo, and migrate into your skin to pigment your hair. These cells slowly die over your lifetime, leading to a loss of that colour.

Many children are born with very fair or pale blonde hair, which often darkens up as they grow. You may have seen photos of people you know now as dark haired adults who had blonde hair as children, which can often be a bit of a surprise. Unfortunately there is no known reason why hair colour changes with age, but there are some good guesses.

One possibility is that it is all to do with our genes. The way your genes are turned on or off changes over time because of the environment you live in. Hair gets fairer in the summer under the sun, but darkens in winter when there is less sun. It could be the food we eat, the shampoo we use or even something in the air around us that affects the way our genes are turned on or off. Our genes and environment work together in complex ways that we are only just beginning to understand. Future genetic research may be able to pinpoint exactly why and how these changes happen.