The best-selling shampoo in the world is Head & Shoulders with about 110 bottles of the anti-dandruff formula sold every minute and 29 million a year. Yet the medicated shampoo market’s size is hardly surprising: at some point, half of us will suffer the unsightly, sometimes uncomfortable condition.

But what causes dandruff? Which of the many products available should you use? And what about theories that these shampoos are bad for the hair, and actually promote flakes? Here experts answer some key questions about problem scalps . 

What is dandruff?

Many of us will have looked down in horror at a fine sprinkling of white flakes on the shoulder of a dark top. But many forms of dandruff do not shed.

Dandruff is characterized by the formation of fine, white or greyish loose skin scales. The epidermis (outer layer of skin) constantly changes and skin cells renew themselves all the time. The cells begin to grow from the base layer deeper in the skin and are gradually pushed to the surface, before coming away from the scalp.

Dandruff occurs when skin cells form too fast, meaning more skin cells are shed and become clumps that can be seen by the naked eye.

“This increased epidermal turnover may be caused or exacerbated by abnormally high levels of a fungus called malassezia globosa, which is a type of yeast and is always found on the scalp, even in those without dandruff,” says British trichologist Tony Maleedy.

Des Tobin, Professor of Cell Biology at the University of Bradford, UK, agrees: “This yeast is strongly implicated in dandruff, though the nature of this relationship between the two isn’t completely clear.

“It may introduce an inflammatory immune response in some people because the yeast produces enzymes capable of causing the scalp’s surface cells to increase their shedding rate.”

Consultant dermatologist Dr. Russell Emerson, at The Hove Skin Clinic, says: “The medical name for dandruff is seborrhoeic dermatitis and in some it can also affect the face.

“We often see dandruff and seborrhoeic dermatitis as a genetic condition in families, particularly if it is severe.

“Those with greasy skin types are most at risk because the yeast likes to grow in sebum.”

What type of dandruff do I have?

There are variations in the severity and form of the condition.

“With some types of dandruff the flakes leave the scalp easily. In other cases, they adhere to the scalp and build up to form a thick covering. With simpler forms of dandruff the scalp is usually a normal color,” says Tony Maleedy. “However, with the more severe forms of the condition there’s an underlying inflammation that renders scalp tissues more tender and sensitive than with simple dandruff.”

Other factors such as stress or diet may also trigger the condition.

“This is because stress increases sebum production,” says Dr. Russell Emerson. “The sebum feeds the yeast.”

Does dandruff shampoo work?

“If the underlying cause isn’t treated properly, the scales will quickly return,” says Tony Maleedy.

“Treatments including ingredients such as coal tar, salicylic acid [Neutrogena T-Gel has both] and selenium sulphide [Selsun Blue] can be considered a little dated compared to the more sophisticated antimicrobials of recent years.”

These work by softening the scales so they can be washed away. However, they have been superseded in effectiveness by shampoos that contain drugs which control the level of micro-organisms on the scalp. These newer options are also less harsh, meaning they can be used often.

Marilyn Sherlock, of The Institute of Trichologists, echoes this advice.

“There are medications that will control this condition,” she says.

“Zinc pyrithione [found in Head & Shoulders, Pantene and chemist own brands] is one of the most common treatments for this condition.”

“Use Head & Shoulders daily for a fortnight,” says Dr. Russel Emerson.

“Then use it two to three times a week as a maintenance treatment.”

If once you start using it less regularly, the dandruff returns, he recommends trying shampoos with ketoconazole.

“Such products [Nizoral, and an own brand at Boots] should be used no more than twice a week between regular shampoos.”

More regular use of ketoconazole may cause skin irritation. If you have tried these two methods and your dandruff persists, visit your GP, who can refer you to a dermatologist. Steroid lotions or creams and antifungal tablets are usually successful in persistent cases.

For facial seborrhoeic dermatitis, a GP may prescribe a topical anti-fungal cream or a combination of a low-strength topical steroid with Daktacort, an anti-fungal.

“Should you suffer from severe dandruff for more than six weeks that doesn’t respond to anti-dandruff shampoos, see your GP,” says Dr. Russell Emerson.

“It may be a more serious problem, such as psoriasis.”

Does washing make it worse?

Some say using anti-dandruff shampoos exacerbates the condition, or that once you start using them you can’t stop as the scalp becomes reliant on the medication.

“This is a myth,” says Dr. Russell Emerson.

“The shampoo has a direct chemical effect on the yeast, but it grows back so you need to maintain use.”

So it’s about controlling the condition, rather than curing it.

Many women are turned off by some formulas as they have a reputation for stripping color from the hair. Again, this is a myth.

Tony Maleedy says: “It may have been true in the past but this had more to do with the basic cleaning agents used. Most leading brands have improved formulations.”

Are there natural options?

“Dandruff is caused by fungi, so treating topically with a hair rinse containing loose-leaf rosemary and tea-tree oil may help,” says medical herbalist Lucy Stephens, from London’s Reva Clinic.

“Rosemary contains anti-fungal essential oils and tea-tree oil has been shown to have anti-fungal activity against a wide range of fungi. Topical aloe-vera gel has also shown improvement in seborrhoeic dermatitis due to its anti-inflammatory properties. Apply it topically at night and rinse in the morning.”

Anti-itch creams such as La Roche Posay Lipikar Baume AP, which contains shea butter and canola oil, can also help.

“Coal-tar shampoo is capable of slowing down the epidermal turnover, which is why it has been used in the treatment of psoriasis and other skin disorders,” says Tony Maleedy.

“Juniper tar [a tree tar] is more effective than coal tar and tends to be used in more modern treatments.”