Seborrheic dermatitis: more than just dandruff
Last updated September 3, 2026.
Seborrheic dermatitis is a chronic inflammatory skin condition that produces red, greasy, flaking patches in the oil-rich zones: scalp, eyebrows, sides of the nose, behind the ears, and chest. In its mildest form it is dandruff; in its full form it is a visible, itchy, recurring rash. It is driven by the skin's reaction to a normal yeast, not by poor hygiene, and it is controlled rather than cured.
What does it look like?
On the scalp: flaking (dandruff), with redness and itch in more active cases. On the face: red, greasy, flaking patches in the eyebrows, the creases beside the nose, the eyelids (blepharitis), and behind the ears. On the chest: a red flaking patch between the pectorals. The flakes are typically yellowish and slightly greasy, unlike the fine dry scale of a simply dry scalp. Severity fluctuates: worse in winter, worse with stress, worse after illness.
Why does it happen?
The trigger is an inflammatory reaction to Malassezia, a yeast that lives on everyone's skin and feeds on skin oils. Why some people react and others do not involves genetics, skin barrier, and immune factors. It is more common and more severe in people with Parkinson's disease and in those with weakened immunity, including HIV. It is not contagious, not an allergy, and not caused by washing too much or too little.
What actually controls it?
- Antifungal shampoos: ketoconazole 2% shampoo two or three times weekly is the anchor treatment for the scalp; selenium sulfide and zinc pyrithione shampoos are effective alternatives. Leave the lather on for 3-5 minutes before rinsing.
- Face and chest: ketoconazole cream for the inflamed patches; the shampoo lather can be used as a short-contact face wash.
- Short steroid courses: a mild topical steroid for a few days settles angry flares; use briefly and on the face with care.
- Maintenance, not cure: once controlled, keep a medicated shampoo in the weekly routine; stopping everything is how the relapse cycle starts.
- Reduce the amplifiers: manage stress where possible, limit heavy greasy products on the scalp, and do not pick at scale.
When is it an emergency?
Seborrheic dermatitis never is. But see a doctor if the rash spreads rapidly or severely, if it does not respond to antifungal shampoo after four weeks, if the eyelids are persistently inflamed, or if it appears severely and suddenly in an adult, which can occasionally signal an underlying condition worth checking. In babies, the same condition appears as cradle cap and follows its own gentler rules. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Is seborrheic dermatitis just bad dandruff?
Dandruff is its mildest form: flaking of the scalp without much inflammation. Seborrheic dermatitis proper adds redness, itch, and greasy scale, and extends beyond the scalp to the eyebrows, nose creases, ears, and chest. Same cause, same treatments, different severity. If your dandruff comes with visible red patches on the face, you have graduated from cosmetic dandruff to seborrheic dermatitis, and the treatment shifts from any anti-dandruff shampoo to a proper antifungal routine.
Why does it keep coming back?
Because the yeast involved, Malassezia, is a permanent resident of normal skin. Treatment suppresses the inflammatory reaction; it does not evict the yeast. Stop treatment and the reaction rebuilds over weeks. The solution is maintenance: once the flare is controlled, keep a medicated shampoo in the rotation once a week or so, indefinitely. Think of it like brushing your teeth: ongoing prevention, not a one-time fix. Stress, winter, and illness will still cause occasional flares, which short steroid courses settle.
Is seborrheic dermatitis contagious or caused by being dirty?
Neither. Malassezia lives on virtually everyone's skin; the condition is your immune system's reaction to it, not an infection you caught. It has no relationship to washing frequency, and it does not pass between people. Family clustering happens because the tendency to react is genetic. The condition is common, affecting around 1 in 20 adults, and it says nothing about your hygiene.
Which shampoo should I use?
Ketoconazole 2% shampoo has the strongest evidence and is the standard anchor. Selenium sulfide and zinc pyrithione shampoos are effective over-the-counter alternatives. Technique matters as much as the product: lather and leave on the scalp for 3-5 minutes before rinsing, two to three times a week during flares, weekly as maintenance. Rotating between two active ingredients helps if one seems to lose effect. For the face, the same shampoo works as a short-contact wash, or use ketoconazole cream.
Can I use steroid cream on my face?
Briefly and mildly, yes; long-term, no. A mild steroid like hydrocortisone 1% for up to a week settles an angry facial flare quickly. But regular or prolonged steroid use on the face thins the skin and can trigger perioral dermatitis, so steroids are a flare tool, not a maintenance strategy. For ongoing facial control, ketoconazole cream and, for stubborn cases, calcineurin inhibitor creams (tacrolimus, pimecrolimus) prescribed by a doctor are the sustainable options.
Is seborrheic dermatitis linked to any other conditions?
Yes, two notable ones. It is significantly more common and more severe in people with Parkinson's disease (the reasons are unclear but the association is strong) and in people with HIV or other causes of weakened immunity, where it can be an early clue. A sudden, severe, or treatment-resistant outbreak in an adult without an obvious explanation is a reasonable prompt for a general health review. For the large majority of people, though, it is simply a standalone skin tendency.