Dandruff vs Seborrheic Dermatitis: Differences, Causes and Medicated Shampoos

Flakes on dark clothing and an itchy scalp are among the most common skin complaints, and the words "dandruff" and "seborrheic dermatitis" are often used as if they meant the same thing. They are closely related. DermNet describes dandruff as a mild, uninflamed form of seborrheic dermatitis on the scalp, and Cleveland Clinic notes that seborrheic dermatitis on a teenager's or adult's scalp is usually just called dandruff. The difference lies mainly in how much inflammation is present and where on the body it appears.

How the two differ

Feature	Dandruff	Seborrheic dermatitis
Where it appears	Scalp	Scalp, eyebrows, sides of the nose, ears, beard, eyelids, chest and skin folds
Scale	Fine, bran-like white flakes	Greasy, white-to-yellow scale, sometimes thick plaques
Redness	No underlying redness	Ill-defined red or salmon-pink patches; on skin of colour, lighter patches may appear instead
Itch	Can be itchy	Itch is usually mild
Care needed	Most people manage it at home with dandruff shampoo (AAD)	Chronic and relapsing in adults, often needing maintenance

These descriptions come from DermNet, Cleveland Clinic and the NHS. DermNet notes that seborrheic dermatitis is sometimes seen together with psoriasis, a combination called sebopsoriasis.

Who gets seborrheic dermatitis

DermNet estimates that it affects about 3% to 12% of people, with two peaks. In babies it shows up as cradle cap, usually in the first three months, and often clears by 6 to 12 months. In adults it is more common in men. Factors linked with it include oily skin, a family history, a weakened immune system, Parkinson's disease and some medicines. Cleveland Clinic adds rosacea, psoriasis and acne to the list of related skin conditions.

Close-up of a man pressing his fingers into the hair at his temple — Dandruff can itch. In seborrheic dermatitis the itch is usually mild. Photo: Towfiqu barbhuiya / Pexels

What causes it

The role of Malassezia

Malassezia is a yeast that lives on everyone's skin and is usually harmless. Cleveland Clinic explains that when too much of it grows, it triggers a skin reaction. The yeast thrives in oily areas, and it produces a substance that converts skin oil into a fatty acid, which irritates the skin and causes redness, itching and flakes. DermNet describes the same process: enzymes from the yeast break down oils in sebum, which may trigger inflammation.

Yeast alone does not explain the whole picture. A review in the International Journal of Cosmetic Science, written by industry scientists, points out that Malassezia is also found on healthy scalps, so it cannot be the only cause. The two species most common on the scalp are M. globosa and M. restricta. The review lists three contributing factors that act together: the yeast, the amount of scalp oil and individual susceptibility.

A weaker skin barrier

That individual susceptibility appears to involve the outer layer of skin. The same review reports that the scalp in dandruff shows depleted barrier lipids, more water loss through the skin and low-level inflammation. Cleveland Clinic similarly notes that over time the irritation weakens the skin's outer barrier.

What does not cause it

The NHS states that dandruff is not caused by poor hygiene, although flakes may be more obvious when hair is washed less often.

Common triggers

Stress and lack of sleep: DermNet lists both as triggers for flares, and the NHS says stress can make dandruff worse.
Season: flares are typically worse in winter and improve in summer (DermNet). The NHS also mentions cold weather.

Hands working a wide brush through a section of coily black hair — For coarse, curly or coily hair, the AAD suggests dandruff shampoo about once a week, on the scalp only. Photo: Xavier Messina / Pexels

The oily scalp connection

Cleveland Clinic notes that Malassezia grows well in oily areas, and DermNet describes seborrheic dermatitis as affecting the parts of the body richest in oil glands, and lists oily skin as a risk factor. The AAD's washing advice reflects this. For fine, straight or oily hair, it suggests washing often, possibly daily, and using a dandruff shampoo about twice a week. For coarse, curly or coily hair, it suggests washing as needed and using a dandruff shampoo about once a week, applied only to the scalp because the active ingredients can dry out hair.

Woman leaning back at a basin while her hair is rinsed and her scalp massaged — Some medicated shampoos need 5 to 10 minutes on the scalp before rinsing. Photo: Oleskandra Biliak / Pexels

Medicated shampoo ingredients

The AAD lists zinc pyrithione, salicylic acid, sulfur, selenium sulfide, ketoconazole and coal tar as ingredients to look for. The NHS names ketoconazole, coal tar and salicylic acid. DermNet and Cleveland Clinic add ciclopirox, an antifungal available on prescription.

Ingredient	What the sources say
Ketoconazole	Antifungal; Cleveland Clinic lists it as a prescription shampoo, while the NHS and AAD list it among dandruff shampoo ingredients. The cosmetic science review notes greater lasting effect and some anti-inflammatory action
Zinc pyrithione	Antifungal; widely used and able to reach into the hair follicle (cosmetic science review)
Selenium sulfide	Antifungal with cytostatic effects, meaning it slows cell growth (cosmetic science review)
Salicylic acid	Listed by the AAD and NHS as a dandruff shampoo ingredient
Coal tar	Listed by the AAD, NHS, DermNet and Cleveland Clinic
Ciclopirox	Prescription antifungal shampoo (DermNet, Cleveland Clinic)

The cosmetic science review reports that an in-use comparison found no significant difference in antifungal effect between selenium sulfide, zinc pyrithione and ketoconazole, and that no well-controlled study has ranked them definitively.

How to use them

Leave it on: the AAD says some shampoos should stay on the scalp for 5 to 10 minutes before rinsing, and Cleveland Clinic suggests at least five minutes.
Rotate: if one shampoo does not help, the AAD suggests alternating between products with different active ingredients.
Give it time: the NHS suggests using an anti-dandruff shampoo for up to four weeks and trying more than one type if needed.
Keep going: DermNet notes that adult seborrheic dermatitis often needs long-term maintenance, and Cleveland Clinic describes it as a condition that comes and goes.

Prescription options

When shampoos are not enough, DermNet and Cleveland Clinic describe short courses of mild steroid treatments, antifungal creams for the face and body, and calcineurin inhibitor creams for longer-term use on the face. Oral antifungals and light therapy are reserved for resistant cases.

When to see a doctor

The NHS recommends a non-urgent GP visit if symptoms continue after at least four weeks of anti-dandruff shampoo, if dandruff is severe or very itchy, if the scalp is red or swollen, or if flaky, itchy patches appear on the face or body. The AAD adds that a dermatologist can check whether flaking is a sign of another condition, such as psoriasis, a scalp fungal infection or eczema.