Seborrheic dermatitis (also called seborrhic dermatitis, seb derm, and SD), is a common skin disease that causes a flaky, white to reddish scales to form on oily areas of the skin. These areas could be the scalp, eyebrows, eyelids, ears, chest, creases of the nose, lips and along skin folds in the middle body.

In adolescents, the disease is often described as dandruff and in infants it is called ‘cradle cap’. In infants, involvement may be extensive, but the condition cures spontaneously when they are 6 to 12 months old.

It is common in adolescents and young adults and rare in the middle aged. However, the reappearance of seborrheic dermatitis after the age of 50 is common. seborrheic dermatitis is prevalent in 1% to 3% of the population and occurs more in men than women. Its incidence is unusually high among AIDS patients, ranging from 35% to 80%.

The lesions in chronic seborrheic dermatitis often worsen in winter. The effect of increased sunlight in summers is unclear. Although there is some evidence to show that sunlight has a beneficial effect on seborrheic dermatitis, psoralen plus type A UV therapy may actually worsen the seborrheic dermatitis condition in some patients.

The relationship between dandruff and seborrheic dermatitis is controversial. Some regard seborrheic dermatitis of the scalp as just severe dandruff. Renewed interest in the role of malassezia yeast in the development of seborrheic dermatitis has provided more proof that dandruff may be, in most cases, a mild form of seborrheic dermatitis.

Seborrheic dermatitis causes

The cause is unknown, though several factors have been implicated. seborrheic dermatitis appears to run in families and is often associated with skin diseases, such as, rosacea, blepharitis, ocular irritation and acne vulgaris. It is also seen with skin diseases associated with growth of the malassezia yeast species.

Seborrheic dermatitis and malasezzia yeasts

Malasezzia yeasts are present on the human skin in small numbers. Increase in the numbers of these yeasts can cause skin problems. The earlier view that malassezia yeasts caused seborrheic dermatitis was given up when no causal link was found and when these yeasts were observed in healthy people, with or without seborrheic dermatitis lesions.

Interest in malassezia yeasts revived when the antifungal ketoconazole was found effective in seborrheic dermatitis treatment. The belief of some researchers that more malassezia yeasts were present in the scalp of patients with seborrheic dermatitis or dandruff was disputed by others. However, the role of these yeasts in seborrheic dermatitis development is difficult to deny in the light of the facts that the antifungal ketoconazole reduces the number of malassezia yeasts and improves the clinical condition of seborrheic dermatitis.

Immune response in seborrheic dermatitis

Since yeast is present in both seborrheic dermatitis affected and healthy people, it was suggested that there was a predisposition to the disease, involving some kind of either an immune or an inflammatory reaction. The T-cell action may be depressed increasing the IgA and IgG levels. But two studies found no increase in IgA levels against the yeasts. It was suggested that the reaction was caused by the yeast themselves, or by toxins produced by them. There is evidence supporting this view.

Seborrheic dermatitis in HIV-positive and AIDS patients is more severe and lesions of the extremities are common. Seborrheic dermatitis severity increases with increased immune deficiency. The different clinical manifestations of seborrheic dermatitis in HIV-positive and AIDS patients have led to suggestions that seborrheic dermatitis in AIDS patients should be regarded as a distinct clinical condition that is secondary to the immune disease.

Hormonal factors

Hormonal factors have also been cited since seborrheic dermatitis frequently appears in the post-puberty stage and is generally confined to areas with more sebaceous glands. Research which shows that human sebocytes respond to androgen stimulation supports this view.

Other diseases associated with seborrheic dermatitis

Neurologic conditions, such as, Parkinson’s disease, head injury and stroke are associated with this disease. Seborrheic dermatitis is also common in people with mood disorders. Why there is a link between seb derm and these conditions is not known, though there is evidence of higher hormonal activity in association with Parkinson’s disease.

Treatment of seborrheic dermatitis

Firstly, good hygiene must be maintained. Ordinary soaps and detergents must not be used, as they dry up the skin and may cause flare-ups. Dermatologists recommend shampoos containing coal tar, ketoconazole, selenium sulfide, or zinc pyrithione.

For severe cases, keratolytic agents and corticosteroids are used. Since the discovery of ketoconazole as an effective remedy for seborrheic dermatitis, better antifungal agents are being sought.

High-potency corticosteroids were once used for their anti-inflammatory action, but are now being discontinued due to adverse effects and they are generally being replaced by low-potency types of corticosteroid.

The non-specific agents used in seborrheic dermatitis treatment include preparations containing selenium sulfide and sulfur. Coal tar is also effective in seborrheic dermatitis. In some European countries oil of cade is used – but this is hard to find in North America. Oil of cade is somewhat like a coal tar preparation.

In more refractive cases, sebosuppressive agents like isotretinoin may be used to reduce sebaceous gland activity.

In infants, the scalp should be frequently washed by an antidandruff shampoo. If scale is extensive in the scalp, the scale may be softened with oil, gently brushed free with a baby hairbrush and then washed clear.