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 trichologist Tony Maleedy.
Des Tobin, Professor of Cell Biology at the University of Bradford, 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 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 colour," says 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 Emerson. "The sebum feeds the yeast."
DOES DANDRUFF SHAMPOO WORK?
"If the underlying cause isn't treated properly, the scales will quickly return," says 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 However, they have been superseded in effectiveness by shampoos that contain drugs which control the level of micro-organisms on the scalp.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 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 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 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 colour from the hair. Again, this is a myth.
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 Maleedy.
"Juniper tar [a tree tar] is more effective than coal tar and tends to be used in more modern treatments."
- Daily Mail
