The exact cause of seborrhoeic dermatitis is not fully understood by doctors. However, factors such as your genes, hormones and changes in your environment are thought to contribute. In this post, we outline what we do currently know about the causes of the condition.

The name is made up of two parts: ‘dermatitis’, which is skin complaint causing redness and itching; and ‘seborrhoeic’, which means the condition affects oily areas of the skin such as the face, scalp and centre of the chest. This is where a higher concentration of your oil-producing sebaceous glands, from which the condition gets the second part of its name, are located.

Seborrhoeic dermatitis is a very common condition, but many people don’t know that they have it. It is thought around 4% of the population may suffer from seborrhoeic dermatitis, with up to 50% of people being affected by dandruff, which is a mild form of the condition affecting the scalp area. The symptoms can range from mild, dry flaking to more severe hardening and reddening of greasy skin in the affected areas.

Anyone can develop seborrhoeic dermatitis (including babies*, a condition known as ‘cradle cap’) but it is most common in people aged between 30 and 60 years old and slightly more common in men than in women.

The exact reasons why some people develop the condition are unclear, but it is thought to be triggered by an overgrowth of a yeast which lives on your skin called Malassezia, or by an overreaction in your immune system towards this yeast. Everyone has Malassezia on their skin, but people with seborrhoeic dermatitis may suffer an increased inflammatory reaction to it, either because they have too much of the yeast or because they are more sensitive to it, leading to symptoms that can include itchiness, soreness and even flaking in the affected areas.