The scalp is among the thickest skin of the body and contains more blood vessels than other parts of the body. Like the face, the scalp also contains a high concentration of sebaceous glands, which produce sebum. Scalp skin is prone to becoming dry and flaky caused by low humidity/temperature, poor scalp hygiene, hair care products, fungal infections (dandruff), psoriasis, eczema, and seborrheic dermatitis.
It is estimated that around 50% of the world population suffers from dandruff. However, most conditions that consumers call dandruff are probably just dry scalp caused by over shampooing, use of excessively hot water during showering, use of products that irritate the skin, low humidity/temperatures or excessive heat when drying. Dry scalp is characterized by small, white flakes of skin cells and dandruff by larger, greasy, or waxy flakes or clusters of skin cells that are usually yellowish or grey. They may come off in your hair brush or stick to your hair or scalp and are frequently accompanied by itching. Often dry scalp can make you more prone to getting dandruff.
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A more severe form of dandruff is sometimes referred to as seborrheic dermatitis. The etiology of dandruff and seborrheic dermatitis appears to be dependent upon three factors: presence of sebum, micro flora metabolism, and individual susceptibility. Dandruff, unlike dry scalp, is usually associated with a fungal infection of the scalp caused by Malassezia furfur. Dandruff is characterized by decreased levels of intercellular lipids in scalp stratum corneum and an impaired barrier function.
Dandruff causes a weakened scalp barrier, which can cause subclinical inflammation and a higher susceptibility to topical irritants. The histamine level in subjects with dandruff is more than twice that in those who do not have dandruff, which may explain the increased itch perception in those patients. Additionally, histamine perturbs the barrier function of the skin while topical antihistamines improve skin barrier repair after tape stripping.
5-lipoxygenase (5-LOX), a key enzyme for the production of the itch and inflammatory mediator leukotriene B4 (LTB4), is increased in the epidermis and around the hair follicles in itchy lesional scalp, suggesting the possibility of the involvement of LTB4 in itch and inflammation observed in dandruff. Topical application of oleic acid to the scalp has been shown to induce a dandruff-like desquamation, which is structurally similar to dandruff. Malassezia furfur on the scalp can metabolize sebum, causing the release of irritating free fatty acids like oleic acid. However, the same dose of oleic acid does not induce flaking in subjects who are not predisposed to dandruff. Squalene in scalp sebum can also oxidize to form squalene hydro peroxide, which can also lead to scalp irritation.
Antidandruff products are monographed OTC drugs in the US. Actives include:
- Zinc Pyrithione (1% rinse off, .1-.25% leave on)
- Sulfur (2-5%)
- Selenium Sulfide (1%)
- Coal tar (.5-5%)
- Salicylic acid (1.8-3%)
- Chapter 12. Dandruff and Seborrheic. Dermatitis: A Head. Scratcher. J.R. Schwartz, Y.M. DeAngelis, T.L. Dawson Jr. www.com/files/pdf/.../TRI_book_chapter_Ch12_Dandruff.pdf
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