Dandruff and Dandruff Shampoos

What is the science behind dandruff? What happens to the skin in dandruff?

All human skin is in a constant state of renewal, whether we have dandruff or not. Skin cells are constantly produced at the bottom of the epidermis (the uppermost layer of the skin) and push towards the surface of the skin. The skin that is visible to us is composed of old dead cells. Thus, the skin is in a constant state of renewal. Shedding of the skin is a normal part of the skin's life cycle whether on the scalp or on other parts of the body. Even though we shed as much as a million skin cells a day, they are usually too small to be visible.

In dandruff, the skin turnover accelerates as much as 10 times the usual rate. With accelerated shedding, skin cells pile on top of each other producing large visible clumps of oily skin on the scalp. It is thought that a fungus called malassezia, plays a role in dandruff. Oleic acid, a biproduct of sebum when metabolized by the fungus, is thought to cause inflammation in the scalp, leading to accelerated skin shedding and dandruff.

  • Skin is constantly renewed. As new skin cells continually push towards the surface, old cells are shed.
  • Normally skin shedding is not visible to the naked eye as the pieces of skin are too small. Under normal circumstances a skin takes approximately 30 days from the time it is produced at the bottom of the epidermis until it sheds at the surface.
  • In dandruff, the production of skin accelerates as much as 10 times the usual rate causing it to clump at the surface into visible pieces. This is generally caused by inflammation.
  • A fungus called malassezia which naturally resides on human scalp is thought to play a major role in dandruff. When it feeds on sebum a natural oil that is produced in the skin, it releases an oil which is thought to cause inflammation of the scalp, causing dandruff.

How do dandruff shampoos treat dandruff?

Although there are numerous active ingredients that help treat dandruff, and many more individual products, all dandruff shampoos attack the problem of dandruff in one of three general ways:

  • Keratolyics such as salicylic acid help the surface skin loosen and shed away easier. These agents help separate the clumps of skin seen in dandruff.
  • Antifungal agents such as zinc pyrithione or ketaconazole reduce the number of malassezia yeasts which are responsible for dandruff proliferation.
  • Steroidal agents help reduce inflammation in the skin and thus, reduce acceleration of skin production.