We need to consider three factors when defining dandruff: our hormones, sebum (a substance found on our scalps) and a micro-organism called Malassezia.

For the majority of us, dandruff problems begin with the onset of puberty. (If there are flakes visible in a child’s hair before puberty it’s worth consulting your doctor as it may indicate a more serious condition.)

During puberty, our bodies start producing much more testosterone. This hormone not only affects hair growth, but also the rate at which we shed dead skin – something we do all the time.

Testosterone can also have a dramatic effect upon the production of sebum, an entirely natural substance linked to hair growth. Sebum is a greasy substance that protects our scalps and makes it difficult for micro-organisms to live there.

However, one organism, called Malassezia, has adapted to live off sebum. Now, there’s no easy way to say this, but Malassezia is a fungus. It’s entirely natural and benign, but it’s still a fungus – one that lives on the areas of our bodies where our skin contains more grease, like the scalp.

Malassezia produces oleic acid which it deposits on our scalps. The way our immune systems respond to this causes inflammation of the top layer of skin and this leads to an increased turnover of skin cells. They also clump together so we see them as flakes of dandruff.

So that’s basically what dandruff is: the scalp’s reaction to Malassezia that leads to a speeding up of your natural cycle of skin replenishment.