Seborrheic dermatitis is a very common, scaling rash that tends to occur in areas where the skin is oily. Commonly affected areas include the scalp (dandruff), eyebrows, eyelids (blepharitis), ears, nasal folds, armpits, and groin. It is a chronic skin condition that can appear any time after puberty, fluctuates in severity, and may persist indefinitely.
Seborrheic dermatitis is usually caused by an overabundance of a normally harmless skin yeast, also called malassezia. The yeast produces toxic substances that irritate the skin and make it itch. Stress and physical illness can lower an individual’s resistance to the yeast.
On the scalp, seborrheic dermatitis appears as dry pink or flesh-colored patches with a yellow scaly surface. The patches may spread to the entire scalp.