Dandruff consists of visible flakes that detach from the outermost layer of the scalp. It results from a disruption in the natural process of skin shedding – which is usually accelerated – and is frequently accompanied by itching, tightness and, at times, widespread redness. Although benign, it can have a significant psychosocial and aesthetic impact.
The scalp is an area rich in hair follicles and sebaceous glands. Under normal circumstances, epidermal cells are renewed every 28 days. In the case of dandruff, this cycle speeds up considerably (sometimes as short as 7 days), leading to the build-up of dead cells that are not shed properly. These clumps form white or yellowish flakes, which may be more or less sticky depending on the nature of the sebum present.
There are two main types of dandruff:
Dry dandruff (pityriasis simplex): Fine, white, flaky, and falls easily onto the shoulders. It often appears on dry or slightly irritated scalps, particularly in winter or in dry climates.
Oily dandruff (pityriasis steatoides): Thicker, yellowish in colour, and tends to stick to the scalp due to excess sebum. It is often associated with mild to moderate inflammation, or even a form of seborrhoeic dermatitis.
Some classifications include other specific forms: dandruff associated with psoriasis, deeper fungal infections, or that caused by irritating cosmetics.
Current research highlights the involvement of several biological factors, notably an impairment of the skin barrier, keratinocyte hyperproliferation, and the proliferation of microorganisms such as Malassezia, a yeast naturally present on the scalp. Its lipase activity produces irritating fatty acids, disrupting the scalp’s balance, particularly when its pH is out of balance (ideally around 5.5).
