|Classification and external resources|
A microscopic image of human dandruff
Dandruff is the shedding of dead skin cells from the scalp. Dandruff should not be confused with a simple dry scalp. As skin cells die a small amount of flaking is normal; about 487,000 cells/cm2 get released normally after detergent treatment. 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 gender and ethnicity. It often causes itching. It has been well 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. Most cases of dandruff can be easily treated with specialized shampoos. There is, however, no true cure.
Those affected by dandruff find that it can cause social or self-esteem problems, indicating treatment for both psychological and physiological reasons.
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. 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 patches on the scalp, skin and clothes.
Dandruff has been shown to be the result of three required factors:
- Skin oil commonly referred to as sebum or sebaceous secretions
- The metabolic by-products of skin micro-organisms (most specifically Malassezia yeasts)
- Individual susceptibility
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 (OA). During dandruff, the levels of Malassezia increase by 1.5 to 2 times its normal level. Penetration by OA of the top layer of the epidermis, the stratum corneum, results in an inflammatory response in susceptible persons which disturbs homeostasis and results in erratic cleavage of stratum corneum cells.
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.
Shampoos use a combination of ingredients to control dandruff. The pathogenesis of dandruff involves hyperproliferation of keratinocytes, resulting in deregulation of keratinization. The corneocytes clump together, manifesting as large flakes of skin. Essentially, keratolytic agents such as salicylic acid and sulphur loosen the attachments between the corneocytes and allow them to get swiped off.
Regulators of keratinization 
Zinc pyrithione (ZPT) heals the scalp by normalizing the epithelial keratinization or sebum production or both. Some studies have shown a significant reduction in the number of yeasts after use of ZPT, which is an antifungal and antibacterial agent. A study by Warner et al. demonstrates a dramatic reduction of structural abnormalities found in dandruff with the use of ZPT; the population abundance of Malassezia decreases, parakeratosis gets eliminated and corneocytes lipid inclusions are diminished.
The parakeratotic properties of topical corticosteroids depend on the structure of the agent, the vehicle and the skin onto which it is used. Corticosteroids work via their anti-inflammatory and antiproliferative effects.
Selenium sulfide 
It is believed that selenium sulfide controls dandruff via its anti Malassezia effect rather than by its antiproliferative effect, although it has an effect in reducing cell turnover. It has anti-seborrheic properties as well as cytostatic effect on cells of the epidermal and follicular epithelium. The excessive oiliness after use of this agent has been reported in many patients as adverse drug effect.
Coal Tar 
Imidazole antifungal agents 
Imidazole topical antifungals such as ketoconazole act by blocking the biosynthesis of ergosterol, the primary sterol derivative of the fungal cell membrane. Changes in membrane permeability caused by ergosterol depletion are incompatible with fungal growth and survival.
Ketoconazole is a broad spectrum, antimycotic agent that is active against both Candida and M. furfur. Of all the imidazoles, ketoconazole has become the leading contender among treatment options because of its effectiveness in treating seborrheic dermatitis as well.
In contrast to the imidazole antifungals, the hydroxypyridones do not affect sterol biosynthesis; instead they interfere with the active transport of essential macromolecule precursor, cell membrane integrity and the respiratory process of cells. Ciclopirox is widely used as an anti-dandruff agent in most preparations.
Black Pepper 
Black pepper contains the dandruff fighting minerals zinc and selenium. In Indian traditional Ayurveda, powdered black pepper has been used to treat dandruff.
Egg oil 
In Indian, Japanese, Unani (Roghan Baiza Murgh), and Chinese traditional medicine, egg oil was traditionally used as a treatment for dandruff, but there is no clinical evidence indicate efficacy for this purpose.
Seborrhoeic dermatitis 
Specific diagnosis and treatment of dandruff may be difficult as its spectrum blurs with those of seborrhoeic dermatitis and some other scale shedding conditions. In seborrhoeic dermatitis redness and itching frequently occurs 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 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 immuno-suppression seem to affect seborrheic dermatitis.
See also 
- Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. ISBN 1-4160-2999-0.
- Ranganathan S, Mukhopadhyay T (2010). "DANDRUFF: THE MOST COMMERCIALLY EXPLOITED SKIN DISEASE". Indian J Dermatol 55 (2): 130–134. doi:10.4103/0019-5154.62734. PMC 2887514. PMID 20606879.
- "A Practical Guide to Scalp Disorders". Journal of Investigative Dermatology Symposium Proceedings. 2007-12. Retrieved 2009-02-06.
- DeAngelis YM, Gemmer CM, Kaczvinsky JR, Kenneally DC, Schwartz JR, Dawson TL (2005). "Three etiologic facets of dandruff and seborrheic dermatitis: Malassezia fungi, sebaceous lipids, and individual sensitivity". J. Investig. Dermatol. Symp. Proc. 10 (3): 295–7. doi:10.1111/j.1087-0024.2005.10119.x. PMID 16382685.
- Ro BI, Dawson TL (2005). "The role of sebaceous gland activity and scalp microfloral metabolism in the etiology of seborrheic dermatitis and dandruff". J. Investig. Dermatol. Symp. Proc. 10 (3): 194–7. doi:10.1111/j.1087-0024.2005.10104.x. PMID 16382662.
- Ashbee HR, Evans EG (2002). "Immunology of Diseases Associated with Malassezia Species". Clin. Microbiol. Rev. 15 (1): 21–57. doi:10.1128/CMR.15.1.21-57.2002. PMC 118058. PMID 11781265.
- Batra R, Boekhout T, Guého E, Cabañes FJ, Dawson TL, Gupta AK (2005). "Malassezia Baillon, emerging clinical yeasts". FEMS Yeast Res. 5 (12): 1101–13. doi:10.1016/j.femsyr.2005.05.006. PMID 16084129.
- Dawson TL (2006). "Malassezia and seborrheic dermatitis: etiology and treatment". Journal of cosmetic science 57 (2): 181–2. PMID 16758556.
- Gemmer CM, DeAngelis YM, Theelen B, Boekhout T, Dawson Jr TL (2002). "Fast, Noninvasive Method for Molecular Detection and Differentiation of Malassezia Yeast Species on Human Skin and Application of the Method to Dandruff Microbiology". J. Clin. Microbiol. 40 (9): 3350–7. doi:10.1128/JCM.40.9.3350-3357.2002. PMC 130704. PMID 12202578.
- Gupta AK, Batra R, Bluhm R, Boekhout T, Dawson TL (2004). "Skin diseases associated with Malassezia species". J. Am. Acad. Dermatol. 51 (5): 785–98. doi:10.1016/j.jaad.2003.12.034. PMID 15523360.
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