Dandruff

Dandruff
A microscopic image of human dandruff
Classification and external resources
Specialty	Dermatology
ICD-9-CM	690.18
DiseasesDB	11911
MeSH	D063807

Dandruff is the shedding of dead skin cells from the scalp.^[1] As skin cells die, a small amount of flaking is normal; about 487,000 cells/cm² are released normally after detergent treatment.^[2] Some people, however, experience an unusually large amount of flaking either chronically or as a result of certain triggers, up to 800,000 cells/cm², which can also be accompanied by redness and irritation.

Dandruff is a common scalp disorder affecting almost half of the population at the post-pubertal age and of any sex and race. It often causes itching. It has been established that keratinocytes play a key role in the expression and generation of immunological reactions during dandruff formation. The severity of dandruff may fluctuate with season as it often worsens in winter.^[2] Dandruff is rare before puberty, peaks in the teens and early twenties, and declines with age thereafter.^[3] Most cases of dandruff can be treated with specialized shampoos. There is, however, no known cure.^[4]

Those affected by dandruff find that it can cause social or self-esteem problems, indicating treatment for both psychological and physiological reasons.^[5]

Signs and symptoms

Typical case of dandruff.

The signs and symptoms of dandruff are an itchy scalp and flakiness.^[6] Red and greasy patches of skin and a tingly feeling on the skin are also symptoms.^[7]

Causes

Dandruff can have several causes, including dry skin, seborrhoeic dermatitis, not cleaning/scrubbing often enough, shampooing too often, psoriasis, eczema, sensitivity to hair care products, or a yeast-like fungus.^[8] Dry skin is the most common cause of flaking dandruff.^[8]

As the epidermal layer continually replaces itself, cells are pushed outward where they eventually 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:^[9]

1. Skin oil commonly referred to as sebum or sebaceous secretions^[10]
2. The metabolic by-products of skin micro-organisms (most specifically Malassezia yeasts)^{[11][12][13][14][15]}
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.^[16]

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,^[17] 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.^[2] 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.^[13]

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 affliction of the 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.^[10] 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.^[18][19]

Seasonal changes, stress, and immuno-suppression seem to affect seborrheic dermatitis.^[2]

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.^[20] 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.^[2]

Treatment

Nizoral (ketoconazole) 2% shampoo

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.^[6] Ketoconazole as a shampoo appears to be the most effective.^[6]

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.^[2]

Ciclopirox is widely used as an anti-dandruff agent in most preparations.^[21]

Coal tar

Coal tar causes the skin to shed dead cells from the top layer and slows skin cell growth.^[22]

Epidemiology

Dandruff affects up to half of adults.^[6]

Etymology

According to the Oxford English Dictionary, the word dandruff is first attested in 1545, but is still of unknown etymology.^[23]

References