What is seborrhoeic dermatitis?
‘Dermatitis’ means an inflammation of the skin; ‘seborrhoeic’ simply means that the rash commonly comes up in areas rich in sebaceous (grease) glands such as the face, scalp and centre of the chest.
Seborrhoeic dermatitis is very common, affecting between 3 and 5% of the global population. It is more common in young adults than during old age and can occur in infants, but then it usually clears up over a few months.
What causes it?
This is not fully understood, although a yeast called Malassezia that lives on the skin plays a part in causing it.
Seborrhoeic dermatitis usually affects people who are otherwise well. However, it is particularly likely to occur in people who have neurological diseases such as Parkinson’s disease, or human immunodeficiency virus (HIV) infection. This indicates that the immune system of those affected with seborrhoeic dermatitis might be involved in one way or the other.
Tiredness and stress can sometimes trigger a flare of seborrhoeic dermatitis. It is more common in cold than in warm weather, and it is not related to diet.
How is it treated?
Seborrhoeic dermatitis does best with treatments that attack the yeasts that live on the surface of everyone’s skin. They are not the same as the yeasts that cause thrush or those that are present in foods.
Is it hereditary?
What are the symptoms of seborrhoeic dermatitis?
Seborrhoeic dermatitis of the scalp can be itchy, sore and the skin can flake off as dandruff. The redness, soreness, itching and scaling can be particularly embarrassing when it occurs on the face.
What does it look like?
The rash is made up of red areas covered with greasy-looking white or yellowish scales. Most commonly, the rash involves just one or two areas, but it can sometimes be extensive. Seborrhoeic dermatitis occurs most often:
- On the scalp: seborrhoeic dermatitis here ranges from a mild flaky scalp (dandruff) to a redder, scalier and sometimes weeping rash. Cradle cap in infants may be a feature of seborrhoeic dermatitis.
- On the face: it often affects the inner parts of the eyebrows, the creases beside the nose and adjacent parts of the cheeks. The eyelids may also become red, sensitive and inflamed (blepharitis).
- In and around the ears: some people have inflammation inside the ear canals, in the cup of the ear and behind the ears. The skin often oozes and crusts in these areas and the ears may swell. Inflammation in the ear canal (otitis externa) can cause it to become blocked.
- On the front of the chest and between the shoulder blades: it shows up as well-defined, roundish red patches that are sometimes scaly.
- In the flexures: it often affects moist areas such as the skin under the breasts, in the groin, under the arms, or in folds of skin on the abdomen. In infants, the nappy area is commonly affected.
How is it diagnosed?
Your doctor will usually be able to make the diagnosis by the look of the rash. No tests are normally necessary and a skin biopsy is seldom needed. If there is any suspicion of scalp ringworm (a fungus infection), your doctor will send a specimen of the scales for culture.
The most common difficulty for general practitioners is distinguishing seborrhoeic dermatitis from psoriasis. Psoriasis of the scalp usually comes up in well-defined rather redder patches, with a whiter, thicker type of scaling.
Can it be cured?
Treatments may keep seborrhoeic dermatitis under control, but they do not cure it.
How can it be treated?
Remember that treatments suppress seborrhoeic dermatitis rather than cure it, and that it often comes back after the treatment has stopped. You may therefore have to use treatments either continuously or on and off for months or even years. The choice of treatment also depends on which parts of the skin have the rash:
- In the scalp: for flaky scalp, medicated shampoos containing agents such as zinc pyrithione, selenium sulphide or ketoconazole can be used regularly. Leave them on for 5 to 10 minutes before rinsing them off. If dense scales cover the scalp, remove these first with warm olive oil. Sometimes a scalp application containg a strong steroid, used sparingly and occasionally, can help reduce itching and redness. Alternatively a salicylic acid-based ointment can be rubbed in at night and washed off in the morning.
- Elsewhere: mild steroid creams and/or an antifungal component are usually effective. Washing your body with an antifungal shampoo containing ketoconazole may also help. Leave the shampoo on for 5 to 10 minutes before rinsing it off. Medicated eardrops may help affected ear canals.
Occasionally, if the rash is widespread or resistant to the treatments listed above, your doctor may suggest a short course of an oral anti-yeast medication.
What can I do?
Once your scalp is clear, continue using an anti-fungal shampoo once a week to reduce the possibility of the rash coming back. A plain moisturiser may help to reduce scaling and redness of the skin. Changing your diet is not likely to make any difference.