What is Dandruff?

Dandruff is a form of seborrheic dermatitis, which is also classically found in the eyebrows and on the sides of the nose. The condition itself is not fully understood, but is thought to be a reaction to varying types of Malassezia, yeast that resides in pretty much everyone's sebaceous glands (which cluster in the affected areas). Although pretty much everyone has the yeast, only certain people seem to react to it regularly. On the scalp this is known as dandruff.

Importantly, there are also forms of psoriasis which can be isolated to the scalp and can cause flaking, which can be indistinguishable on clinical exam but respond to treatment differently as it likely is not secondary to the yeast implicated in seborrheic dermatitis. Tar and salicyclic acid compounds (Tsal and Tgel) have shown mild relief in the improvement of psorasis, and can help people with mild scalp psoriasis. These will have limited effect in seborrheic dermatitis.

Now as for seborrheic dermatitis, there are two treatment options. One is to reduce the burden of the yeast and the second is to try to damp down the body's abnormal immune response against it (which is causing the inflammation and scaling).

Ketoconazole (Nizoral) cream and shampoo tend to work fantastically for this with limited side effects. Prescription strength is 2%, over the counter is 1%. People usually start 2-3 times weekly, leaving in form fives minutes, for a few weeks dropping to once weekly when under control. This alone often solves the problem. Alternating with selenium sulfide shampoos (ie Head and shoulders) can also help.

Alternatively, mild topical steroids can be prescribed (we usually give hydrocortisone 2.5% cream, although the 1% is over the counter) to reduce inflammation, but there can be long term side effects to its use such as skin thinning, hypopigmentation and telangiectasia so I usually stick with ketoconazole given the paucity of side effects.

Once you understand the condition, you might ask why cool water showers helps control it versus hot water. Short answer, it likely doesn't. Hot water can dehydrate our skin more, make you itchier and in particularly cause flaring with eczema, but does not plan a major role in the pathogenesis of seborrheic dermatitis.