What is Seborrhoeic Dermatitis?
Seborrhoeic (sometimes spelt seborrheic) dermatitis is a chronic, flaking skin condition which most commonly occurs on the face and scalp. It occurs in about 5% of western societies and is slightly more prevalent in men.
Not a lot is known about the skin condition despite a reasonable body of research. Some believe it is related to another flaking skin condition, psoriasis. Patients with seborrhoeic dermatitis are frequently misdiagnosed with having psoriasis, however its distribution is different from psoriasis. Both conditions commonly occur on the scalp however. A histology (pathology) report will often come back with a diagnosis of ‘seb-psoriasis’ as they can appear very similar.
Others believe it is a type of dermatitis – a condition that is quite different from psoriasis.
It is not unusual for seborrhoeic dermatitis to occur on the face with other skin conditions such as acne or rosacea. This further confuses the diagnosis.
Pityriasis versicolour – a condition found mainly on the chest and upper arms, can also occur with seborrhoeic dermatitis.
Prevalence of Seborrhoeic Dermatitis
The condition can affect people from infancy and within the first 3 months of life. This is often referred to as cradle cap. At this age it has been found that 10 percent of boys and 9.5 percent of girls have the condition. This type of seborrhoeic dermatitis usually resolves spontaneously within the first 12 months and without treatment.
In some cases the flaking condition occurs on other parts of the infant’s body however generalized seborrheic dermatitis is uncommon in otherwise healthy children. Usually it can be linked with an immunodeficiency, failure to thrive, diarrhoea or nutritional deficiencies. In infants it is believed that an altered essential fatty acid pattern may be important in the pathogenesis of the condition (transient impaired function of the delta-6 desaturase enzyme).
Seborrhoeic dermatitis often shows up at around puberty so there is possibly a hormonal link. Its incidence peaks at around 40 years of age but commonly occurs in adults between 30 and 60 years of age.
Where does it occur?
The scalp and face are the most common areas for seborrhoeic dermatitis to occur. Behind and inside the ears is a common place. The brows are particularly prone to redness and flaky scales.
Unlike rosacea, seborrhoeic dermatitis occurs in the nasofacial folds and the nasolabial folds (the smile lines).
Seborrhoeic Dermatitis can sometimes progress down from the scalp to the lower nape of the neck and the forehead. The beard area and chin can also be affected. Some people can also develop inflammation of the eyelids (blepharitis).
On the body the condition can occur on the sternal (chest) area and interscapular areas. It can also be found in the flexures of the axillae, groin, anogenital region around the umbilicus (belly button) and the mammary skin (under the breast).
What does it look like?
The condition is usually symmetrical (both sides of the body) in its distribution. The area underlying the seborrhoeic dermatitis can be red and somewhat well demarcated. The area of erythema (redness) is nowhere near as demarcated as that of psoriasis however.
The scale is sometimes described as yellowish and greasy (especially on the scalp), however around the brow, it is most usually a dry, white/clear scale. In comparison, the scale of psoriasis tends to be thicker and more silvery in colour.
On the chest, it can appear as small red-brown lesions known as papules. They are follicular and perifollicular i.e. they occur around the hair follicles. This distribution on the chest is sometimes known as medallion seborrhoeic dermatitis as the red papules resemble the shape of a flower or medallion.
Another form of seborrhoeic dermatitis that occurs on the chest, resembles pityriasis. It has macules (rather than papules) that are flat and red lesions.
What is the cause?
There is little conclusive evidence regarding the cause however research has revealed the following as contributing factors;
- Increased sebaceous and hormonal (androgen) activity
- The skin of people with seborrhoeic dermatitis has a high lipid (fat) content compared to people who do not have seborrhoeic dermatitis
- Nutritional problems i.e Oxidative stress may be present
- Nutrient deficiencies
- A problem with the processing of biotin
- A fungal infection with the presenceof Pityrosporum ovale or P. orbiculare (also known as Malassezia yeast). Malassezia yeast is a part of the normal micro flora of the skin, however under some conditions it is believed to trigger skin conditions such as acne, rosacea, dandruff, seborrhoeic dermatitis, atopic dermatitis, psoriasis and pityriasis versicolour. The metabolites of the Malassezia specifies irritate the free fatty acids released from the sebaceous triglycerides. Increased free fatty acids produce scalp flaking and an itchy skin. This susceptibility is an individual thing- some people will be prone to it whilst others will not.
- Genetic factors
- An altered immune response. People with severely depressed immune conditions such as AIDS can have a more generalized distribution of seborrhoeic dermatitis
- The presence of inflammation
- Generalized seborrheic dermatitis-like eruption associated with acquired immunodeficiency syndrome.
- High stress and anxiety. People with seborrhoeic dermatitis were found to have a high anxiety score. Stress is a major trigger of all skin conditions including seborrhoeic dermatitis (find out more about the effects of stress upon the skin). It is believed that stress contributes to inflammation via its effect upon the hypothalamic-pituitary-adrenal axis. This triggers the release of neuropeptides, neurotrophins, lymphokines and other chemical mediators from nerve endings and dermal cells. Dermal mast cells are known to release mediators that are pro-inflammatory (producing a ‘fire within’).