Dandruff is the term that is usually applied to ordinary scaling of the skin of the scalp.  It is not a disease; it is part of a normal process of shedding cells from the surface of the skin.  However, cells shed from the body cannot be seen, whereas in the hair they can and therefore they are of cosmetic interest.  People with dandruff seem to shed surface cells on their scalp more quickly that people without dandruff and the cells that are shed clump together and are visible.  Dandruff can be a long-time condition that keeps coming back when treatment is stopped.  The condition is associated with the yeast Pityrosporum ovale. Excessive dandruff may be associated with skin disorders such as eczema or psoriasis and with a condition called seborrhoeic dermatitis (or seborrhoeic eczema).

Treatment

There is no cure for dandruff, only control.  Any detergent shampoo is of use in treating ordinary dandruff.  If used at least two or three times a week, a detergent shampoo will keep the hair clean of dandruff but of course a detergent shampoo will not prevent the production of scales by the scalp.

The scalp should be well massaged, the shampoo left in contact with the scalp for several minutes and then thoroughly washed off.  Any shampoo left on the scalp may cause the dandruff to stick together and be even more visible.

Detergent antiseptics are sometimes used in shampoos (e.g. benzalkonium and cetrimide) although the antiseptic effects have never been shown to be beneficial over and above the detergent effects.

Drug additives in shampoos

Shampoos that contain drugs to treat dandruff are often referred to as medicated shampoos.  Certain drug additives are included in shampoos because they may reduce the production of cells from the skin of the scalp, dissolve the particles of dandruff or break them up into smaller pieces, relieve itching and/or act as an antiseptic.

Ketoconazole is extremely effective in the treatment of dandruff, (available as a 2% shampoo).  The shampoo should be used twice a week for 2 -4 weeks, after which its use can be reduced to weekly or fortnightly as needed, to prevent it coming back.

Reducing the production of dandruff

Selenium sulphide (Selsun) and zinc pyrithione (Head and Shoulders) reduce the rate of growth of cells on the scalp and this may help to reduce dandruff formation.  Because their effectiveness depends upon the time that they are in contact with the scalp, these shampoos should remain in contact with the scalp for a total of 4-6 minutes before being washed off.  However, this length of time for contact with the scalp must be balanced against the fact that prolonged contact increases the risk of developing harmful effects.

Selenium sulphide should be rinsed from the hair thoroughly, otherwise it may discolour it.  Frequent use produces an odour and an oily scalp.  It may ‘burn’ the skin under the finger nails and irritate the eyes.  The hands and nails should be thoroughly washed after use.  It should not be used within 48 hours of applying hair colouring or permanent wave preparations.  Selenium sulphide is dangerous if swallowed.

Zinc pyrithione also kills bacteria and fungi, and although it is insoluble and not absorbed through the skin, it should not be used on damaged skin.  It may, rarely, cause contact dermatitis.

Breaking up dandruff particles

Preparations that break up and loosen dandruff particles contain keratolytics, which dissolve the cement that holds the cells together.  They include sulphur, salicyclic acid and allantoin; they all rely on a reasonable amount of contact time with the skin and yet with shampoos the contact time is usually minimal.  However, ointments and pastes are not acceptable because they are messy; therefore preparations in water or alcohol are used.  They may be moderately effective in controlling dandruff but they can irritate the skin and the eyes.  Resorcinol should not be used because it may be absorbed from  broken skin and affect the thyroid gland.

WARNING: Products that break up dandruff particles also act on keratin in the hair, which may damage the hair.

Tar products

Tar products break up the dandruff but they smell and they may stain the skin and hair.  They also make the skin sensitive to sunlight.  However, they are useful for treating psoriasis of the scalp.

Anti-itching preparations

These include menthol, eucalyptol, phenol, resorcinol, pine tar and methylsalicylate.  They may irritate the skin and eyes, and be harmful if they are swallowed. The temporary relief from itching which they may produce has no real part to play in the treatment of dandruff.

WARNING: Corticosteroid applications (e.g. hydrocortisone) should not be used to treat itching associated with ordinary dandruff.

Anti-infective preparations

The antiseptics cresol, thymol and phenol are included in some shampoos.  They may irritate the scalp and are of very doubtful benefit because there appears to be no relationship between infection and dandruff.

It is important to understand that the treatment will not cure dandruff permanently and that it is important to use the treatment on a less frequent basis to prevent the dandruff coming back.

It is the scalp that needs to be treated rather than the hair.  So treatments should be applied to the scalp and massaged gently.  All products should be left in the scalp for 5 minutes before rinsing.  It is debateable whether dandruff is caused by infrequent hair washing, but it is generally agreed that frequent washing (at least three times a week) is an important part of managing dandruff.

Between treatments an ordinary shampoo can be used.