It is a common form of skin eczema that occurs in parts of the body with high oil (sebum) production. Body areas that are commonly affected include the scalp, ears, face, chest, and folds of skin, such as the underarms or the skin below breasts or overhanging abdominal folds. The cause of seborrhea is unknown, although a yeast that often lives on the skin, Malassezia furfur, may play a role.
One common manifestation of seborrhea that affects the scalp is dandruff. Scalp seborrhea can also present as thick, flaky, localized patches of scale. On the face, seborrhea produces reddish-brown, dry-looking, or thick, greasy scales on the eyebrows, sides of the nose, and behind the ears. Reddish, scaly patches may also appear in the folds of skin mentioned above. Although skin affected by seborrhea may feel "dry," moisturizing only makes them redder.
Scalp seborrhea and dandruff do not cause permanent hair loss. Often, scalp seborrhea doesn't even itch significantly. Seborrhea can appear during infancy, starting shortly after birth and lasting several months. It may affect the scalp ("cradle cap") or produce scaly patches on the body. Adults of all ages may develop seborrhea, too, especially on the scalp and face.
Some people who have weakened immune systems, such as those on chemotherapy or those with HIV disease or certain neurological disorders, may have very severe seborrhea. It is important to emphasize, however, that seborrhea is a very common condition, affecting perhaps 5% of the population (with men predominating). The vast majority of those who have it are completely healthy and have no internal or immune problems.
Symptoms of dandruff include flaky scales that range in color from white to yellow, usually on oily parts of the skin such as the scalp or inside of the ear. Sometimes the affected skin is also red.
Common symptoms of dandruff
You may experience fluctuations in dandruff symptoms, with extended inactive periods between flare-ups.
Symptoms during flare-ups usually include:
- Dry, white, flaking skin.
- Itchy skin.
- Oily, yellow, adhering scales of skin.
- Plaque (broad, raised area of skin).
- Redness, warmth or swelling.
- Skin lesions (any abnormal skin tissue).
- Symptoms that might indicate a serious condition.
In some cases, dandruff can be part of severe seborrheic eczema, severe psoriasis, or blepharitis (inflammation of the eyelids) that should be immediately evaluated in an emergency setting.
Seek prompt medical care if you have any of these serious symptoms including:
- Burning sensation in the eye.
- Eye pain.
- Eyelashes that grow abnormally or fall out.
- Flaking or crusted eyelids.
- Gritty feeling in the eye.
- Increased sensitivity to light.
- Itchy eyes.
- Lip inflammation.
- Oozing, wet skin.
- Red, sore eyes (bloodshot eyes).
As the epidermal layer continually replaces itself, cells are pushed outward where they eventually die and flake off. In most people, 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.
During dandruff, the levels of Malassezia increase by 1.5 to 2 times its normal level. Malassezia globosa, that metabolizes triglyceridespresent in sebum by the expression of lipase, resulting in a lipid byproduct oleic acid (OA). Penetration by OA of the top layer of the epidermis, thestratum corneum, results in an inflammatory response in susceptible persons which disturbs homeostasis and results in erratic cleavage of stratum corneum cells.
Rarely, dandruff can be a manifestation of an allergic reaction to chemicals in hair gels, sprays, and shampoos, hair oils, or sometimes even dandruff medications like ketoconazole.
There is some evidence that excessive perspiration and climate have significant roles in the pathogenesis of dandruff.
Treatment of seborrhea (dandruff) is directed at fighting the skin inflammation. This is done either directly, by using cortisone-based creams and lotions (which reduce inflammation), or by reducing the yeast that builds up on scaly areas and adds to the problem. Note, though, that seborrhea is not a yeast infection.
What doesn't help dandruff?
- Moisturizing: Moisturizing lotions don't do much more than smooth out scales and make patches look redder.
- Switching brands of shampoo: Shampoo doesn't cause dandruff. However, medicated shampoos (see below) can help.
- Changing hair-care routines: There is no "right" shampoo or conditioner, nor is there a "correct" number of times to shampoo per week; seborrhea and dandruff are not caused by excessive shampooing "drying out the scalp." Hair dyes and conditioners do not cause or aggravate dandruff.
- Switching antiperspirants: When underarms are red from seborrhea, almost anything will make them redder, including antiperspirants, even though they are only aggravating the seborrhea and not causing it.