Dandruff is increased turnover of skin cells on the scalp, leading to large amounts of flaking, and possibly redness and itching. In people with dandruff, skin cells develop and die in 2-7 days, in contrast to a cycle of one month in people with no dandruff. It is a condition that can fluctuate depending on the season, usually becoming worse in winter. Half of the population is affected by dandruff at some point; in people older than 50 it is not very common.
There is no real cure for dandruff yet.
Three factors are required for dandruff to appear [Ro and Dawson]:
- metabolic waste of skin bacteria (specifically Malassezia globosa yeast) [Gupta et al.]
- individual susceptibility (above two combined will not necessarily cause dandruff in non-susceptible people)
M. globosa has no ability to manufacture its own fatty acids, which are essential for life, and so relies on human sebum for its source. The way it causes dandruff:
- The fungus produces 8 types of lipase and 3 types of phospholipase enzymes, which help to break down sebum into free fatty acids and glycerol.
- It feeds on the saturated fatty acids, while it leaves irritating unsaturated oleic acid behind.
- The oleic acid then penetrates the scalp, irritates the skin and triggers faster turnover of skin cells in susceptible people.
- This has been proven by removing all of the fungus and treating the scalp with pure oleic acid in susceptible and non-susceptible individuals.
- The difference between susceptible and non-susceptible individuals is unclear.
- Blood group O subjects may be the most susceptible, followed by AB group. [Shankar et al.] Also it's more common in males.
- Note: olive oil is extremely high in oleic acid, does this mean that putting olive oil on the scalp will exacerbate dandruff?
- Note 2: the fungus research seems to be mainly done by Head & Shoulders, so likely some details of it is not revealed.
- Note 3: a collection of a lot of research: link
- Avoid putting fats on the scalp. Saturated fat feeds the fungus, and unsaturated (oleic acid) directly trigger dandruff in susceptible people.
- Avoid using alkaline soap, baking soda, and similar, as the fungus grows optimally in pH 7-9 [Vijayakumar et al.]
- Consequently, raising the acidity on the scalp may be helpful; there are plenty of reports that apple cider vinegar on the scalp relieves itching.