Most people probably assume the strange grey fluff caught in a hairbrush is nothing more than lint.It is the sort of thing that tends to get ignored, even by people who are otherwise fairly strict about their beauty routine. Make-up brushes get washed, pillowcases go in the laundry, and skincare gets carefully rotated, but the humble hairbrush often escapes the same level of attention.That may be because the build-up looks relatively harmless at first. Sitting between the bristles, it can easily pass for dust or loose fibres picked up from the bathroom or bedroom.What’s more, because it gathers slowly, it is easy to dismiss it as one of those minor cleaning jobs that can always wait until next week.

However, experts say the reality is far less innocent.According to celebrity hairstylist Dean Banowetz, who spoke to Reader’s Digest, it’s ‘a mix of hair, scalp oils, dead skin cells and dust from the air’, with leftover styling product playing a major role in binding it all together.Dermatologist Dr Anna Chacon also explained how the build-up forms, saying: “When we brush our hair, it’s typical for hair to shed, and it can get tangled in the brush.”That, mixed with dead skin cells, which are also naturally shedded, create some buildup, and if you have applied haircare products to your hair, those products can also transfer to the brush.”Top that with dust or other environmental factors, and you get the fuzz.”In other words, the grey mass sitting in your brush is not just household fluff. It is a mixture of shed hair, skin, oils, environmental debris, and old product residue being collected in one place. Lovely.The reason that this is a big deal is that it not only looks unpleasant, but as Banowetz also warned: “It holds onto bacteria and yeast, which can transfer back to your scalp.”