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
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.
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
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 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.