CAUSES OF DANDRUFF (3)

Seborrhoeic dermatitis

You know you have Seborrhoeic dermatitis when there are greasy, red, itchy patches on the skin covered with flaky scales that are white or yellow in color. On the scalp, the condition presents as severe dandruff with some shedding of hair. Other affected areas are the sebaceous-gland-rich areas of your skin such as eyebrows, the sides of the nose, backs of your ears, chest, groin and occasionally the armpits.

Looking at your skin under a microscope, you will see your tormentor, the microscopic yeast, Malassezia. It produces toxic substances that irritate and inflame the skin. Although Malassezia grow on the skin of healthy people as well, scalp swabs from sufferers with seborrheic dermatitis show higher levels of colonization. Under the right conditions, Malassezia will morph from a benign organism into a pathogenic one. Further evidence of this is that the condition improves with antifungal treatment, accompanied by a decrease in numbers of Malassezia on the skin.

Certain illnesses

If you have eczema anywhere on your body, it could also be on your scalp, possibly leading to the development of dandruff.

Shedding of dead skin from the scalp of Psoriasis sufferers may be interpreted as dandruff. Malassezia may play a role in psoriasis on the face and scalp.

People with compromised immune system such as those with HIV-AIDS and neuropsychiatrically impaired individuals have a higher incidence of the condition.

Other diseases that increase your chance of developing dandruff are: Autoimmune and neurological disorders such as Parkinson's disease and systemic lupus erythematosus; Atopic dermatitis, Pityriasis rosea, Tinea capitis, Polycystic ovary syndrome etc.

Genetics

Some of the above diseases have genetic basis. Studies have found that people who are sensitive to yeast have a slightly higher risk of having dandruff. There may be a genetic predisposition for them to be more vulnerable to yeast infection.

Another study found an ABO blood group predisposition. A large number of people screened in the study were carriers of Malassezia species, but only a very small group had dandruff. The researchers concluded this clearly establishes the fact that a benign yeast can transform and become saprophytic to feed on dead skin of some individuals in the population. However, they have not established the triggers for the transformation to occur.

Males are more susceptible to dandruff than females. Researchers have shown that testosterone stimulates the growth of certain dermatophytes (infectious fungi on keratin), while estrogen inhibits the same.

INFECTION

Since Malassezia is frequently associated with dandruff, let us take another look at this organism. It was first identified as yeast found on the skin of patients with dandruff in the 19^th century. Bizarrely, this organism can morphs into a fungal (hyphal) form and/or both. Its hyphal form predominates in skin diseases such as tinea versicolor and Pityrosporum folliculitis.

The hyphae filaments used to be called 'Malassezia' and the yeast forms were called 'Pityrosporum' because scientists thought they were two different organisms.   Then in the 1980s, molecular methods of species identification showed they were two forms of the same organism. Malassezia don’t have the ability to make its own saturated fats. Therefore, it feeds on saturated fats on our skin. In its fungal form, it feeds on our dead skin as well.

Like the chicken and egg question, scientists could not determine whether abundant dandruff on our skin encourages Malassezia to proliferate or increased yeast cells irritates our skin and triggers increased scaling.

However, predisposing factors to Malassezia skin disease include:  

• Warm, humid condition, including sweating. Hence, pityriasis versicolor is common in tropical areas.
• Oily skin hence it is found mainly on oil-gland-rich areas such as the scalp, face and upper trunk.

Frederick Manuel and S Ranganathan postulated “on Two Stages of Dandruff” that “Malassezia colonization is a secondary event in dandruff. And

Suggested that a cascade of events preclude dandruff formation”

The two stages in infection of dandruff sufferers are:-

Stage 1

• At the Primary stage, there are multiple host-specific predisposing factors.
• Multiple nonspecific factors can trigger dandruff. They are of non-microbial origin.

Stage 2

• The secondary stage has multiple microbial causes.
• Response varies according to each individual.

(International Journal of Trichology, 2011)