Seborrheic dermatitis: Clinic, diagnosis and treatment

• Seborrheic dermatitis is an inflammatory skin condition characterized by red, scaly, itchy patches located preferentially in areas rich in sebaceous (seborrheic) glands: scalp, face – mainly the T-zone –, chest area, and back¹.
• It is a very common benign condition that affects between 1 and 8% of the general population, with a higher prevalence in men and the elderly².
• Like atopic dermatitis, seborrheic dermatitis has wide geographic disparities¹.
• In France, it affects 1-3% of adolescents and adults⁶.
• SD can have a strong impact on the quality of life of patients: discomfort, stigmatization, loss of self-esteem, and a limited social life².
• The exact causes of seborrheic dermatitis are not fully understood, but a combination of factors contribute to its development¹.

The causes of seborrheic dermatitis are multifactorial and involve the interaction of three factors:

• The presence on the skin of yeast of the genus Malassezia.
• Sebaceous secretions.
• The immunological profile.

The role of Malassezia yeast in SD^1,5,8

• This type of yeast is commonly found on the skin. Its presence alone is not enough to trigger seborrheic dermatitis.
• However, in some individuals with an impaired skin barrier, the metabolites released by Malassezia on the scalp are responsible for the skin scaling observed in SD.
• The presence of Malassezia in these individuals also causes local inflammation associated with itching.
• The strong correlation between the reduction of Malassezia and the reduction of symptoms associated with SD makes it the preferred target for the treatment of this condition.

The role of sebaceous secretions in SD^4,8

A set of arguments identifies sebaceous secretions as participating in the physiopathology of SD:

• More prevalent in adolescence (more active sebaceous glands).
• Lesions due to SD localized in areas of the body rich in sebaceous glands.
• Lipid composition of the skin surface of men with SD differs from that of unaffected controls.
• Greater presence of Malassezia in areas of greatest sebaceous secretion.

While these arguments support a role for sebaceous secretions in the development of SD, the details of their involvement remain unknown.

Immune factors involved in SD⁴

• The involvement of the immune system is demonstrated in particular by the much higher frequency of SD in immunocompromised patients (organ transplants, HIV, chronic alcoholic pancreatitis, hepatitis C and various malignancies), with rates of up to 83%, compared to 1-3% in the general population.
• However, the details of the mechanism of action are yet to be identified.

Other factors

• Seborrheic dermatitis is more common in men than in women, and the incidence of SD increases in males during adolescence and young adulthood. This suggests an important role for hormones (especially androgens) in its development⁴.
• Stress also plays an important role in the onset of relapses without correlating with a depressive state of the patients. On the other hand, patients in whom stress is likely to cause a relapse, have a higher anxiety score than other patients with SD¹⁰.
• The involvement of genetic factors in SD is less documented than in psoriasis or atopic dermatitis.
• A recent cross-sectional study (2018) including 4,050 participants, 609 of whom had SD (15%), nevertheless identified a correlation between SD and genetic variations that may be involved in inflammation, immunity, or certain skin properties⁷.

The clinical presentation of seborrheic dermatitis is different in infants and in adults.

Newborn and infant^11,17

Infantile seborrheic dermatitis appears towards the end of the 1st or 2nd month and lasts approximately 4 to 6 months. It appears as squamous erythema or crusty eruptions. It can present itself:

• As in adults, in the form of bipolar involvement (scalp and face): greasy, thick, white and yellowish scales (cradle cap).

• In the breech area: breech dermatitis.

• In the folds of the neck and armpits: greasy scales of the axillary folds (possible).
• Absence of pruritus.
• A generalized erythroderma (called Leiner-Moussous) may appear on rare occasions. It often has a positive outcome.

Adult^11,17

• Non-infiltrated, bilateral and symmetrical erythemato-squamous lesions.
• Facial lesions present in 88% of patients, in the form of erythematous patches that may be covered with greasy scales on the nasolabial folds, eyebrows, glabella, and the anterior edge of the scalp. In men, the beard and moustache may be the site of lesions.

• Scalp lesions affect 70% of patients. Most of the time, they are not very severe (pityriasis capitis) but may cause itching.
• Involvement of the trunk in about 27% of patients, in the form of annular or circular plaques on the presternal region.
• Extensive or severe forms:
  • Lesions on the chin and ciliary margins of the eyelids (seborrheic blepharitis) are possible.
  • Pityriasis rosea: severe form of seborrheic dermatitis of the scalp, with the appearance of a helmet surrounding tufts of hair.