Bacteria behind dandruff severity

Bacteria may be the culprits behind your flaky scalp, a new study suggests, not fungi.

A team from Japan and China found dandruff, which afflicts around half the world’s population, is more strongly linked to populations of two bacterial groups – Propionibacterium and Staphylococcus – than the Malassezia fungus, which also happily colonises the human scalp and is widely believed to be the main cause of the condition.

Most dandruff studies have focused on Malassezia. There are 14 known species of Malassezia, with two – M. restricta and M. globosa – linked to skin diseases.

But they’re not the only microbes living in your hair. Bacteria like it there too. It’s warm and full of food. Fungi and bacteria chow down saturated fatty acids found in sebum, the oily substance secreted from the scalp.

So Menghui Zheng from Shanghai Jiao Tong University in China and colleagues swabbed the scalps of 59 Chinese men and women, aged 18 to 60, 48 hours after washing with a non-anti-dandruff shampoo to ascertain sebum levels and bacterial and fungal populations.

Dermatologists also judged the subjects’ dandruff levels using the adherent scalp flaking scale which scores dandruff on a scale of zero to eight.

They found, as expected, older people had more dandruff. The dominant fungus was Malassezia, and the main bacterial populations were Propionibacterium and Staphylococcus. No surprise there either.

But Malassezia levels weren’t associated with dandruff levels. Instead, Propionibacterium and Staphylococcus held greater sway over scalp flakiness. Compared to normal scalps, those with dandruff housed lower levels of Propionibacterium and more Staphylococcus.

This mutual inhibition, the researchers write, has been shown before: the bacteria each exude or meditate processes that make life difficult for the other.

Addressing bacterial imbalance, they suggest, by boosting Propionibacterium and suppressing Staphylococcus may provide a more effective dandruff remedy for those with severe cases than antifungals.

The study was published in Scientific Reports.