|Classification and external resources|
Seborrheic dermatitis (also seborrhea, sebopsoriasis, seborrheic eczema, dandruff, and pityriasis capitis) is a chronic, relapsing and usually mild dermatitis. In infants seborrheic dermatitis is called cradle cap.
Seborrheic dermatitis is an inflammatory skin disorder affecting the scalp, face, and torso. Typically, seborrheic dermatitis presents with scaly, flaky, itchy, and red skin. It particularly affects the sebaceous-gland-rich areas of skin. In adolescents and adults, seborrhoeic dermatitis usually presents as scalp scaling similar to dandruff or as mild to marked erythema of the nasolabial fold.
Signs and symptoms
Seborrhoeic dermatitis' symptoms appear gradually and usually the first signs are flaky skin and scalp. Symptoms occur most commonly anywhere on the skin of the face, behind the ears and in areas where the skin folds. Flakes may be yellow, white or grayish. Redness and flaking may also occur on the skin near the eyelashes, on the forehead, around the sides of the nose, and the chest and upper back.
In more severe cases, yellowish to reddish scaly pimples appear along the hairline, behind the ears, in the ear canal, on the eyebrows, on the bridge of the nose, around the nose, on the chest, and on the upper back.
Commonly, patients experience mild redness, scaly skin lesions and in some cases hair loss. Other symptoms include patchy scaling or thick crusts on the scalp, red, greasy skin covered with flaky white or yellow scales, itching, soreness and yellow or white scales that may attach to the hair shaft.
Seborrheic dermatitis can occur in infants younger than three months and it causes a thick, oily, yellowish crust around the hairline and on the scalp. Itching is not common among infants. Frequently, a stubborn diaper rash accompanies the scalp rash. Usually, when it occurs in infants the condition resolves itself within days and with no treatment.
In adults, symptoms of seborrheic dermatitis may last from few weeks to years. Many patients experience alternating periods of inflammation. The condition is referred to a specialist when self-care has proven unsuccessful.
While the specific causes are not known at this point in time, seborrhoeic dermatitis is not caused by seborrhoea, a pathologic overproduction of sebum.  Instead, the excrement rate of sebum in women was found to be decreased by a significant amount, while men experienced normal rates.  Current theories for the cause of the disease include a weakened immune system, the lack of specific nutrients, or issues with the nervous system. 
The main species found on the scalp is Malassezia globosa, others being Malassezia furfur (formerly known as Pityrosporum ovale) and Malassezia restricta. The yeast produces toxic substances that irritate and inflame the skin. Patients with seborrhoeic dermatitis appear to have a reduced resistance to the yeast. However, the colonization rate of affected skin may be lower than that of unaffected skin.
Only saturated fatty acids (FAs) have been shown to support Malassezia growth. It has also been shown that while number density of M. globosa and M. restricta do not directly correlate to dandruff presence or severity, removal correlates directly with amelioration of flaking. Furthermore, in dandruff-susceptible individuals pure oleic acid, an unsaturated FA and Malassezia metabolite, induces flaking in the absence of Malassezia by direct effects on the host skin barrier. These findings support the following hypothesis:
Malassezia hydrolyze human sebum, releasing a mixture of saturated and unsaturated fatty acids. They take up the required saturated FAs, leaving behind unsaturated FAs. The unsaturated FAs penetrate the stratum corneum. Because of their non-uniform structure, they breach the skin's barrier function. This barrier breach induces an irritation response, leading to dandruff and seborrheic dermatitis.[unreliable source?]
Seborrhoeic dermatitis may be aggravated by illness, psychological stress, fatigue, sleep deprivation, change of season and reduced general health.
Those with immunodeficiency (especially infection with HIV) and with neurological disorders such as Parkinson's disease (for which the condition is an autonomic sign) and stroke are particularly prone to it.
- Coal tar (can be very effective, but, although no significant increased risk of cancer in human treatment with coal tar shampoos has been found, caution is advised since coal tar is carcinogenic in animals, and heavy human occupational exposures do increase cancer risks)
- Isotretinoin As a last resort in refractory disease, sebosuppressive agent isotretinoin may be used to reduce sebaceous gland activity. However, isotretinoin has potentially serious side effects and few patients with seborrhea are appropriate candidates for therapy.
- Aloe Vera applied topically
- Tea tree oil: diluted to 5% applied topically
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