Adult seborrhoeic dermatitis starts at any time after puberty and affects 3-5 per cent of adults. Men are more likely to have it than women: a German study found 4.6 per cent of men and 1.4 per cent of women had the condition. However, dandruff is a mild form of scalp seborrheic dermatitis experienced by nearly half of adults.11,12,13

Red, itchy and flaky skin occurs where there are higher concentrations of sebaceous glands, including the scalp, face and centre of the chest and on the back, particularly in men. The scalp may develop into a weeping rash.11,13,14

Eyebrows, eye lids (blepharitis), skin in and around the ear, and skin around the nose can all become inflamed and flaky. Infection may cause weeping and crusting to form, and can cause a blockage in the ear canal (otitis externa).11

Seborrhoeic dermatitis in infants is usually limited to a few months. It appears on the scalp as cradle cap with waxy scales sticking to hair, but can also appear on the face, in the nappy area and in flexures. It isn’t normally itchy so will not disturb the baby. If it appears to be itchy it could be atopic dermatitis.11,15,16

Malassezia yeast overgrowth or an over-reaction by the skin to the yeast is usually implicated. Stress or tiredness can trigger flare ups, and it is more likely to occur during cold rather than warm weather. The condition can be more severe or long-lasting with certain co-morbidities such as HIV infection or Parkinson’s disease.11