‘Dermatitis’ is a red, itchy, flaky (inflamed) skin; ‘seborrhoeic’ means that the rash affects greasy (sebaceous) skin zones such as the face, scalp and centre of the chest. Seborrhoeic dermatitis is very common in babies and presents as cradle cap of the scalp, a raw, red rash in the nappy area as well as an inflamed skin in the flexures (for example in the neck or under the arms).
It is thought that seborrhoeic dermatitis is triggered by an overgrowth of a harmless yeast called Malassezia that lives on the skin, or an over-reaction by the skin’s immune system to this yeast. These are not the same as the yeasts that cause thrush or those that are present in foods.