A detailed overview on a major fungal infection associated condition - seborrheic dermatitis

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Seborrheic Dermatitis
Seborrheic dermatitis is not an infectious disease in itself, but it can involve infection and a proliferation of fungus in the development of the disease. Seborrheic dermatitis is first and foremost a skin condition, but it can also involve temporary hair loss if the associated infection is located on the scalp or other hair growing areas of the body. As such seborrheic dermatitis doesn’t just develop in hair. The disease and any associated fungal or yeast infection is not only located commonly on the scalp, but also on the sides of nose, eyebrows, ears, and chest. The dermatitis presents as scaly, sometimes oily, inflamed skin that can be itchy or even painful to touch. The extent of flaking and inflammation may vary from person to person.

In infants, the dermatitis and associated infectious disease is called 'cradle cap' but generally the condition becomes evident only during the time of puberty as hormones begin to be expressed in the body. However, in black African-Americans the dermatitis and fungal infection is more common in infants rather than in teens and adults. Apart from Seborrheic dermatitis there are other hair diseases which have severe effects and are more prevalent in the African-American population.

Generally, the seborrheic dermatitis and fungal infections are largely observed in the scalp of young people, and it is relatively rare in middle age. In patients over the age of 50 years, however, seborrheic dermatitis and its promotion of fungal infection again becomes quite common. Also, it is more common in men than in women. Caucasian seniors, particularly of Celtic descent, are most susceptible to this fungal infection compared to other ethnic groups.

Causes of seborrheic dermatitis
The cause of seborrheic dermatitis is not well understood, although there does seem to be a genetic component in the promotion of fungal infection. The species of Malassezia yeasts is considered as the cause of seborrheic dermatitis by some dermatologists but it is still quite a debated aspect. Other dermatologists delieve that a yeast infection does not cause seborrheic dermatitis, but the yeast does like the environment that seborrheic dermatitis creates and it proliferates and further exacerbates the condition.

Around the time of puberty there is a remarkable change in the production scale of lipids. Yeasts and fungi probably prefer lipid-rich areas of the body (like the face, scalp, trunk etc) to grow. The lipids are a rich source of food and the more food available the more fungi, yeasts, and bacteria can proliferate. The yeasts and fungi feed on lipids using enzymes called lipases. These lipases breaks the lipids and release arachidonic acid as part of the digestion process. Arachidonic acid is a skin irritant. The presence of the skin irritant causes the inflammation of skin.

As the yeast proliferates in seborrheic dermatitis there is a major irritation and inflammation on the scalp. Hair follicles find inflamed skin an unhealthy environment and hence normal hair growth is been retarded. The inflamed follicles may enter a telogen resting state and the hair fiber may shed. Thus seborrheic dermatitis may non-specifically cause diffuse hair loss.

Seborrheic dermatitis can also be observed in some new born babies when maternal androgen hormones are passed from the mother to the baby across the placenta. Conditions like Parkinson's disease, head injury, and stroke can also be associated with seborrheic dermatitis, and things like stress and chronic fatigue can make it worse.

Also the dermatitis and any associated infection is commonly aggravated by changes in humidity or seasonal changes.

In seborrheic dermatitis the scalp appearance varies from mild, patchy scaling to widespread, thick, adherent crusts. The formation of plaques is rare in this disease. Skin lesions manifest as greasy scaling over red, inflamed skin.

In black African-Americans seborrheic dermatitis can result in Hypopigmentation - a lack of melanin pigment production in the skin. It leads to the formation thick, yellowish, dry scales on the scalp with associated reddening. Occasionally, there is a localized plaque if the condition develops in the posterior part of the scalp.

The incidence of seborrheic dermatitis is unusually high among patients with AIDS. It leads to the occurrence of severe lesions in the scalp. As the immune deficiency in the patients becomes worse due to AIDS, the lesions of seborrheic dermatitis also become worse. The disease is also more commonly associated with congestive heart failure, Parkinson’s disease, and conditions that cause immunosuppression in premature infants.

Association with dandruff
The association between seborrheic dermatitis and dandruff is controversial. Some dermatologists use the term 'seborrheic dermatitis of the scalp’ as a way of describing severe dandruff. Others believe that the term ‘‘dandruff’’ should be used for any flaking of the scalp, regardless of the causes or origins.

The controversy regarding the relation between these two and any associated fungal infection has become all the more intense as a recent study has observed the role of Malassezia yeasts in the development of seborrheic dermatitis. Malassezia yeasts have been a suspected cause of dandruff for more than a century.

Treatment with nontoxic hair care products
There are several treatments for seborrheic dermatitis. The simplest treatment involves the use of nontoxic hair care products like medicated anti-dandruff shampoos. These shampoos will control the skin proliferation and scaling. Shampoos for seborrheic dermatitis may contain sulfur, selenium sulfide, zinc pyrithione, tar, salicylic acid, or oil of Cade. These shampoos are largely popular nontoxic hair care products which are able to treat the infectious disease.

More recently Azole chemical based shampoos (Ketoconazole - Nizoral) have been made available over the counter. Other similar medicated shampoos may contain fluconazole. All can be effective in treating seborrheic dermatitis. Some dermatologists may also prescribe antibiotics to control the reddening of the greasy patches that cause inflammation.

Seborrheic dermatitis can be a very persistent condition once it starts. So patience is required along with continuous treatment. Preventive treatment should be continued even when the symptoms are gone to stop the condition from coming back.

Aditya K. Gupta, Robyn Bluhm, Elizabeth A. Cooper, Richard C. Summerbell, Roma Batra, “Seborrheic dermatitis”, 2003, Dermatol Clin 21 401–412

Amy J. McMichael,”Hair and scalp disorders in ethnic populations”, (2003), Dermatol Clin 21 629–644

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