Background

Seborrheic dermatitis is characterized by greasy yellowish scale on a background of erythema.  It occurs in areas with lots of sebaceous glands including the scalp, external ear, central face, upper trunk, underarms, and groin.  Its most common and mildest form is dandruff—whitish scale of the scalp and other hair-bearing areas without any underlying erythema.

Seborrheic dermatitis is a chronic and relapsing condition that can be diagnosed clinically.  It tends to be worse in colder, drier climates and improves during summer months—especially with ultraviolet exposure.  Stress can also play a role in initiating or worsening flares.  Individuals with seborrheic dermatitis have an overabundance of Malassezia, a yeast that is normally found on the skin.

Why some people get seborrheic dermatitis and others do not is not clear, but the reason likely has to do with differences in immune responses to Malassezia.  Interestingly, Malassezia has been shown to have immune cross-reactivity with Candida—yeast commonly found in the GI tract.  People with seborrheic dermatitis have been found to have increased levels of Candida antigen in their stools and on the tongue, suggesting that they may have higher levels in their GI tract.  Additionally, seborrheic dermatitis does improve in some patients treated with oral anti-yeast medications.¹

Seborrheic dermatitis can be more extensive and difficult to treat in people with Parkinson’s and HIV; treating these conditions can lead to improvement in the seborrheic dermatitis.