Dandruff

**Dandruff** is a skin condition that mainly affects the scalp. Symptoms include flaking and sometimes mild itchiness. It can result in social or self-esteem problems. A more severe form of the condition, which includes inflammation of the skin, is known as seborrhoeic dermatitis.

The cause is unclear but believed to involve a number of genetic and environmental factors. The condition may worsen in the winter. It is not due to poor hygiene. The underlying mechanism involves the excessive growth of skin cells. Diagnosis is based on symptoms.

There is no known cure. The typical treatment is with antifungal cream such as ketoconazole. Dandruff affects about half of adults. Onset is usually at puberty. Males are more often affected than females. Rates decrease after the age of 50.

## Signs and symptoms

The signs and symptoms of dandruff are an itchy scalp and flakiness. Red and greasy patches of skin and a tingly feeling on the skin are also symptoms.

## Causes

The cause is unclear but believed to involve a number of genetic and environmental factors. The condition may worsen in the winter. It is not due to poor hygiene.

As the skin layers continually replace themselves, cells are pushed outward where they die and flake off. For most individuals, these flakes of skin are too small to be visible. However, certain conditions cause cell turnover to be unusually rapid, especially in the scalp. It is hypothesized that for people with dandruff, skin cells may mature and be shed in 2–7 days, as opposed to around a month in people without dandruff. The result is that dead skin cells are shed in large, oily clumps, which appear as white or grayish flakes on the scalp, skin and clothes.

According to one study, dandruff has been shown to be possibly the result of three factors:

1. Skin oil commonly referred to as sebum or sebaceous secretions
2. The metabolic by-products of skin micro-organisms (most specifically Malassezia yeasts)
3. Individual susceptibility and allergy sensitivity.

### Microorganisms

According to a 2016 study, bacteria (mainly Propionibacterium and Staphylococcus) are more important to dandruff formation than fungi. Bacterial presence was in turn influenced by water and sebum amount.

Older literature cites the fungus *Malassezia furfur* (previously known as *Pityrosporum ovale*) as the cause of dandruff. While this species does occur naturally on the skin surface of both healthy people and those with dandruff, in 2007 it was discovered that the responsible agent is a scalp specific fungus, *Malassezia globosa*, that metabolizes triglycerides present in sebum by the expression of lipase, resulting in a lipid byproduct oleic acid. During dandruff, the levels of *Malassezia* increase by 1.5 to 2 times its normal level. Oleic acid penetrates the top layer of the epidermis, the stratum corneum, and evokes an inflammatory response in susceptible people which disturbs homeostasis and results in erratic cleavage of stratum corneum cells.

### Seborrhoeic dermatitis

In seborrhoeic dermatitis, redness and itching frequently occur around the folds of the nose and eyebrow areas, not just the scalp. Dry, thick, well-defined lesions consisting of large, silvery scales may be traced to the less common condition of scalp psoriasis. Inflammation can be characterized by redness, heat, pain, swelling and can cause sensitivity.

Inflammation and extension of scaling outside the scalp exclude the diagnosis of dandruff from seborrhoeic dermatitis. However, many reports suggest a clear link between the two clinical entities - the mildest form of the clinical presentation of seborrhoeic dermatitis as dandruff, where the inflammation is minimal and remain subclinical.

Seasonal changes, stress, and immunosuppression seem to affect seborrheic dermatitis.

## Mechanism

Dandruff scale is a cluster of corneocytes, which have retained a large degree of cohesion with one another and detach as such from the surface of the stratum corneum. A corneocyte is a protein complex that is made of tiny threads of keratin in an organised matrix. The size and abundance of scales are heterogeneous from one site to another and over time. Parakeratotic cells often make up part of dandruff. Their numbers are related to the severity of the clinical manifestations, which may also be influenced by seborrhea.

## Treatment

Shampoos use a combination of special ingredients to control dandruff.

### Antifungals

Antifungal treatments including ketoconazole, zinc pyrithione and selenium disulfide have been found to be effective. Ketoconazole appears to have a longer duration of effect. Ketoconazole is a broad spectrum antimycotic agent that is active against *Candida* and *M. furfur*. Of all the antifungals of the imidazole class, ketoconazole has become the leading contender among treatment options because of its effectiveness in treating seborrheic dermatitis as well.

Ciclopirox is widely used as an anti-dandruff agent in most preparations.

### Coal tar

Coal tar causes the skin to shed dead cells from the top layer and slows skin cell growth.

## Epidemiology

Dandruff affects around half of all adults.