Scientists have come a little closer to understanding the mysteries of dandruff, a condition as ubiquitous as it is embarrassing.

In the past, dandruff has been blamed on dry skin, oily skin, washing the hair too often or not enough, on diet, stress or simply a lack of personal hygiene. “Dandruff on the collar” is shorthand for a man careless of his personal appearance.

But the real blame for dandruff lies not in neglect but in a yeast-like fungus, Malassezia globosa, which lives on the scalp in millions and feeds on the oily products of the sebaceous glands.

For the first time, scientists have decoded the complete DNA of the fungus, which could provide clues to how to combat it more effectively. The scientists involved work for Procter & Gamble, manufacturers of Head & Shoulders, a successful anti-dandruff shampoo. The fungus is one of the simplest ever sequenced, with just 4,285 genes, 300 times fewer than its human host.

The team responsible, led by Dr Thomas Dawson from Procter & Gamble’s Miami Valley Innovation Centre in Cincinnati, Ohio, report in Proceedings of the National Academy of Sciences that the fungus has adapted to its environment by losing the ability to make its own fatty acids.

Instead, it survives by feeding off the fats secreted on to the scalp by the sebaceous glands. Men have larger sebaceous glands than women, which probably explains why they suffer more dandruff.

The white snow-like flakes of dandruff are actually skin. Shedding skin is normal, but in dandruff sufferers this happens more rapidly than normal.

The newly decoded genome shows that the fungus produces quantities of enzymes called lipases. These trigger dandruff, it is believed, by a two-stage process.

First, the fungus uses lipases to metabolise the fats secreted by the sebaceous glands, creating oleic acid as a by-product. This in turn penetrates the top layer of skin and triggers the rapid turnover of skin cells in susceptible people. This is dandruff.

About half the human population suffers from dandruff, though it can usually be controlled by special shampoos that combat the fungus. Yet despite its importance, relatively little has been known about the fungus that starts the whole process off.

As well as decoding its genome, the P&G team investigated which proteins the fungus secretes. They found that it produces eight lipases and three phospholipases, which it uses to digest the oils from the scalp.

Each of these proteins could, they suggest, be a possible therapeutic target for new anti-dandruff preparations.

They also found that M. globosa has the genes necessary for mating, although happily this has never been observed in the species. The idea of a head covered in fungi is bad enough without having to think of them mating.

Analysis of the genome also suggests something about the origin of the fungus. Its closest relation genetically is a yeast fungus, so it looks as if there was a shift, millions of years ago, from plants to the scalps of human beings, The average human head provides a home for up to ten million M. globosa fungi. Similar fungi cause skin and ear problems in animals, including dogs. Anti-dandruff shampoos do not eradicate the fungus. but they do control it.

Dr Dawson, said: “A complete genomic sequencing of a Malassezia genome opens tremendous opportunities for researchers to understand the mechanisms of fungal species in both humans and nature.

“It’s amazing that the understanding of the genetic make-up of a microscopic organism can have broad implications ranging from human health to agricultural science.”

Dozens of old wives’ cures for dandruff exist, from massaging olive oil, lemon juice, old tea leaves or even vodka into the scalp to adding herbs such as burdock and celandine to your shampoo.

There is no clear evidence that any of these works, prompting the old joke: “What do I recommend for dandruff? Wear a white coat.”

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