It is a chronic inflammatory skin disease that causes outbreaks
Seborrheic dermatitis (also called sebopsoriasis, seborrheic eczema or pityriasis capitis) is a chronic inflammatory skin disease that occurs in outbreaks.
It frequently affects the scalp, in the form of desquamation, which sometimes takes on a yellowish tone, more or less adhered to the scalp. “Dandruff” is the colloquial term to describe what we technically call seborrheic dermatitis.
It can be itchy and, regardless of the scalp, this condition can also affect seborrheic areas such as the face or chest. On the face, it very characteristically affects the nasolabial fold, the glabella, and the eyebrows. Sometimes it also appears on the eyelids, in which case it is called seborrheic blepharitis. In men it is not uncommon to see it also in the beard area.
Babies’ skin is more seborrheic during the first months of life, the result of circulating androgens that passed through the placenta during pregnancy into their bloodstream. For this reason, up to 10% of babies under 3-4 months of age may have seborrheic dermatitis on the scalp (called cradle cap), face, chest, or diaper area.
For what is this?
The exact cause of seborrheic dermatitis is not known. Despite its name, sebaceous production is not increased nor is it specifically a disease of the glands that produce it. It is thought that the skin lesions of seborrheic dermatitis are due to inflammation secondary to the presence of the malassezia fungus, present in the sebaceous areas of the skin. In this way, sebaceous production would favor the proliferation of this fungus and, indirectly, the appearance of lesions.
Fungi of the genus malassezia are saprophytic on human skin. The species specifically implicated in seborrheic dermatitis are malassezia globosa and malassezia restricta. It is likely that the lipases from these fungi break down the sebum on the skin surface, giving rise to molecules such as oleic acid, malasezzin or indole-3 carbaldehyde.
These molecules have an irritant capacity and induce an inflammatory process that will give rise to the characteristic lesions of seborrheic dermatitis. This hypothesis is supported because, as we will see later, the condition improves with the use of antifungals.