Seborrheic dermatitis and dandruff: why they appear, how to treat them, and why they keep coming back

What is seborrheic dermatitis?

Seborrheic dermatitis is an inflammatory condition that preferentially affects areas of the skin rich in sebaceous glands. The best-known location is the scalp, but it can also appear on the eyebrows, the glabella, the sides of the nose, the beard, the ears and behind them, the central chest, and other skin folds.

On the scalp it can cause dandruff, flaking, itching, redness, and in more severe cases, inflammatory plaques with yellowish or greasy scales. The diagnosis is usually clinical, based on the appearance, distribution, and progression of the lesions.

Are dandruff and seborrheic dermatitis the same thing?

They are closely related, but they are not exactly synonymous. We can think of dandruff as the mildest expression on the spectrum of seborrheic dermatitis of the scalp: flaking predominates and there may be little or no visible redness.

In seborrheic dermatitis proper, we more commonly find flaking, inflammation, erythema, itching, and discomfort. There is therefore a continuum ranging from mild dandruff to more inflammatory seborrheic dermatitis, and current literature considers both entities to be closely related within the same clinical spectrum.

Does dandruff appear because I don't wash my hair often enough?

No. Dandruff does not mean poor hygiene. Washing infrequently can allow sebum, scales, and cosmetic products to accumulate and make the flaking far more visible, but that does not mean a person has seborrheic dermatitis because they 'don't wash their hair properly'.

What we are dealing with is a condition in which the microbiome, sebum, the skin barrier, the immune response, and individual predisposition all play a role. It is not a matter of being dirty: it is biology.

What role does Malassezia play?

This is where we find one of the most fascinating aspects. Malassezia is a genus of yeasts that normally forms part of our skin's microbiome. This means something fundamental: having Malassezia does not mean being infected, and all of us can harbour these yeasts without having seborrheic dermatitis.

Malassezia is particularly interesting because it is lipophilic — that is, it is highly adapted to living in lipid-rich environments. That is why we frequently find certain species in sebaceous areas such as the scalp, the face, and the upper trunk.

So does Malassezia cause seborrheic dermatitis?

The most rigorous answer is: it plays a part, but it does not explain the entire condition on its own. For many years the explanation was relatively straightforward — more Malassezia, more seborrheic dermatitis — but today we know the situation is considerably more complex. Malassezia can metabolise components of sebum through enzymes such as lipases and generate substances capable of interacting with the skin barrier and promoting inflammation in susceptible individuals.

However, modern studies show that the quantity of yeast does not correlate perfectly with the severity of the disease. A 2024 review specifically proposes moving away from a view exclusively centered on Malassezia and also considering epidermal barrier dysfunction, the host immune response, the microbiome, inflammation, and sebum. The best way to understand it would be: Malassezia, plus sebum, plus the skin barrier, plus the immune response.

Why does a normal yeast cause problems only in some people?

Because the microorganism is only one part of the equation. Two people can both have Malassezia on their scalp: one presents absolutely no problem whatsoever, while the other develops itching, inflammation, and flaking. The difference probably lies in how the microorganism, the lipids, the skin barrier, and each person's immune system interact with one another.

It is a concept we encounter continually in medicine: what matters is not only which microorganisms we carry, but also how our body responds to them.

Is seborrheic dermatitis a fungal infection?

We should not describe it simply as 'a fungal infection.' Malassezia is a yeast, but it is normally part of the skin's flora. Seborrheic dermatitis is fundamentally an inflammatory disease associated with an abnormal interaction between the skin, sebum, the microbiome, and the immune response.

This explains an apparent paradox: we use antifungals and they work, but we are not trying to sterilize the skin — rather, we are modifying one of the factors involved in the inflammation.

Is seborrheic dermatitis contagious?

No. It is not transmitted by sharing a pillow, touching someone's hair, using the same sofa, hugging, or living with someone. Malassezia is normally part of our skin microbiota. Therefore, seborrheic dermatitis is not a contagious disease.

Why does it cause flaking?

Inflammation disrupts the normal functioning of the epidermis: the cells in the outer layer renew and shed differently, and when many cells shed together, we can see them. That is dandruff.

The scales can be white, fine, and dry, or more yellowish, greasy, and adherent, depending on the severity of the condition and the characteristics of the scalp.

Does having oily hair mean having seborrheic dermatitis?

No. One person may produce a great deal of sebum and not have dermatitis, while another may have seborrheic dermatitis without feeling that their hair is particularly oily. Sebum creates a favorable environment for Malassezia and is part of the pathophysiology, but oiliness does not equal disease: we also need individual susceptibility and inflammation.

Why does it appear mainly on the scalp, eyebrows, and nose?

Because these are particularly sebaceous areas. Seborrheic dermatitis has a characteristic distribution in areas rich in sebaceous glands. That is why we can simultaneously find dandruff on the scalp, flaking between the eyebrows, redness around the nose, scales behind the ears, and flaking inside or around the beard.

This distribution can be a very useful diagnostic clue.

Why does it keep coming back?

Because seborrheic dermatitis tends to be chronic and recurrent. We can perfectly control a flare-up — the itching, flaking, and redness disappear — but that does not mean we have permanently eliminated the predisposition, the microbiome, sebum production, barrier characteristics, and the immune response. That is why it can return.

The 2024 international consensus on scalp seborrheic dermatitis defines it precisely as a chronic and recurrent inflammatory disease, and puts forward differentiated strategies for controlling the flare-up and subsequently maintaining remission.

Does that mean there is no cure?

I prefer to explain it a different way. We do not usually talk about 'curing it forever,' but rather about controlling it. It is similar to many inflammatory skin diseases: we can achieve long symptom-free periods, far less intense flare-ups, less itching, less flaking, and a better quality of life.

But we must accept that it may reappear, and that does not mean the previous treatment was useless.

Can stress make seborrheic dermatitis worse?

Many people say: 'when I am stressed, I get dandruff.' It is plausible and clinically common for flare-ups to coincide with periods of stress, fatigue, or sleep disturbances; DermNet specifically includes stressful events and lack of sleep among the factors associated with exacerbations.

But we must avoid an oversimplified explanation: seborrheic dermatitis is not a psychological disease. Stress can modulate immunity, inflammation, the skin barrier, behavior, and sleep, and may act as a modulating factor — not necessarily the cause.

Can winter make it worse?

Yes. Many people experience worsening during autumn and winter and improvement at certain times of the year. Changes in temperature, humidity, environmental exposure, and daily routines can all have an influence.

However, the pattern is individual: not all patients follow exactly the same seasonal pattern.

How is scalp seborrheic dermatitis treated?

We need to target the main components: Malassezia, flaking, and inflammation. That is why we primarily use antifungal shampoos, keratolytic treatments when necessary, and topical anti-inflammatory agents during certain flare-ups.

The 2024 international consensus and subsequent European recommendations place topical antifungal and anti-inflammatory treatments at the very centre of management.

Which antifungal shampoos work?

Among the active ingredients used are ketoconazole, ciclopirox and selenium sulfide, alongside other anti-dandruff formulations. Ketoconazole and ciclopirox have clinical evidence against seborrhoeic dermatitis: a systematic review found superior efficacy over placebo for both agents, although the quality and duration of the available studies vary.

A comparative trial of 350 patients found that both ciclopirox and ketoconazole significantly improved scalp seborrhoeic dermatitis compared with placebo.

How does ketoconazole work?

Ketoconazole is an azole antifungal that reduces the activity of yeasts such as Malassezia. By reducing this component we can decrease scaling, itching and inflammation. A 2024 review concluded that ketoconazole shampoo has numerous studies demonstrating improvement in scaling and the symptoms of scalp seborrhoeic dermatitis, with good overall tolerability.

But, again, it does not permanently eliminate Malassezia from our skin — nor would we want it to.

How should a treatment shampoo be used correctly?

This detail may seem trivial, but it can make a very significant difference to the outcome. A medicated shampoo should not be used as though we simply wanted to cleanse the hair: it needs to come into contact with the scalp, not just the hair. We must distribute it over the affected areas and respect the contact time indicated for the product, because if we apply it and rinse it off immediately, we may reduce its efficacy.

The frequency depends on the active ingredient, the concentration, the severity, the phase of treatment and the individual response. It is therefore advisable to follow the product's instructions or those given by a healthcare professional.

Do I need to wash my hair less often if I have seborrhoeic dermatitis?

Not necessarily. There is a myth that 'washing too often produces more grease', and as a result some patients with seborrhoeic dermatitis try to go many days without washing their scalp. This can encourage the build-up of sebum, flakes, products and residue, and make the problem more visible or uncomfortable.

The frequency of washing should be adapted to hair type, the amount of sebum, physical activity, the products used and the treatment. But having seborrhoeic dermatitis does not mean we should avoid washing the scalp.

Can I wash my hair every day?

In certain patients, yes — particularly when the scalp is very oily or suitable gentle products are used. The important thing is not to pursue a universal rule of 'once every seven days' or 'every single day without fail': frequency must be tailored to the individual patient.

What we should avoid is a scalp that is permanently irritated, scratched, covered in residue, or treated with overly harsh products.

Do you need to use ketoconazole every day?

Not necessarily. Antifungal shampoos are usually used intermittently. During a flare-up, a higher frequency may be used depending on the product and the indication; afterwards, we can reduce it and switch to a maintenance strategy.

Current consensus emphasizes precisely the importance of separating flare-up treatment from relapse prevention.

What do we do when there is a lot of inflammation and itching?

Sometimes controlling Malassezia alone is not enough. If the scalp is very red, very inflamed, and very itchy, we may temporarily need an anti-inflammatory treatment. Among the options are certain topical corticosteroids, which can be very effective at rapidly reducing inflammation, relieving itching, and bringing the flare-up under control.

But we generally use them for limited periods, not indefinitely as a cosmetic shampoo. Prolonged and inappropriate use of topical corticosteroids can produce adverse effects, so their potency, vehicle, area of application, and duration must be tailored to the patient.

Do corticosteroids cure seborrheic dermatitis?

No. They control inflammation and can achieve rapid improvement during a flare-up, but they do not permanently alter the predisposition, the microbiome, sebum production, or the skin barrier.

That is why we must avoid falling into the habit of 'every time I get dandruff, I use a corticosteroid indefinitely.' Treatment must follow a strategy.

Are there alternatives to corticosteroids for the face?

Yes. In certain facial areas, topical calcineurin inhibitors such as tacrolimus or pimecrolimus may be used, depending on the case. They can be especially useful when we need to control inflammation in specific areas without repeatedly resorting to corticosteroids.

Recommendations on Malassezia-related conditions include both antifungals and short courses of corticosteroids or calcineurin inhibitors for the inflammatory component. The indication depends on the area, severity, age, diagnosis, and clinical history.

Does selenium sulfide work?

Yes. Selenium sulfide is another classic ingredient used against dandruff and seborrheic dermatitis. A recent comparative clinical trial evaluated a shampoo containing 1% selenium disulfide versus 2% ketoconazole in moderate-to-severe scalp seborrheic dermatitis, confirming clinical improvements with both approaches.

Recent recommendations also consider it a useful option due to its antifungal, keratolytic, and sebostatic properties.

What do keratolytics do?

When there are many adherent scales, we can use substances that help remove them, such as salicylic acid. Keratolytics help loosen the excess stratum corneum, which can improve flaking and facilitate the penetration of other treatments.

But we must remember that removing scales does not mean the disease has been fully treated. If we only remove the dandruff without controlling the inflammation and the other underlying mechanisms, it will come back.

Should I pick off the scales with my nails?

No. Scratching the scalp vigorously can cause excoriations, inflammation, small wounds, crusts, and secondary infection, and it can also increase itching. A vicious cycle is then created: itching, scratching, inflammation, and more itching.

Our goal is to control the cause of the pruritus, not to mechanically pick off each individual scale.

Does seborrheic dermatitis cause hair loss?

This is a very common question. Seborrheic dermatitis is not a scarring alopecia — that is, it does not normally permanently destroy the hair follicle. However, a severely inflamed, itchy, and scratched scalp can be associated with a transient increase in shedding or breakage and can make a coexisting alopecia more noticeable.

But if a person is experiencing progressive loss of density, a receding hairline, widening of the part, hairless patches, or scarred areas, we should not automatically explain everything away by saying 'it's just dandruff': another form of alopecia may be coexisting.

Can seborrheic dermatitis coexist with androgenetic alopecia?

Yes, and it is common to find several problems simultaneously. A person can have seborrheic dermatitis as well as androgenetic alopecia. Treating the dermatitis can improve the itching, flaking, inflammation, and overall scalp quality.

But we should not promise that an antifungal shampoo will reverse an established androgenetic alopecia: they are different conditions that can coexist.

Is ketoconazole useful for growing hair?

It should not be used as a substitute for a specific treatment for alopecia. There are studies and scientific discussions regarding the possible effects of ketoconazole on certain scalp conditions, but the solid evidence for its use relates to seborrheic dermatitis and conditions associated with Malassezia.

Therefore, an anti-dandruff shampoo is not a universal treatment for hair loss.

How do you differentiate between seborrheic dermatitis and scalp psoriasis?

They can look very similar. Psoriasis tends to produce more well-defined, thicker plaques with more abundant scaling, can extend beyond the hairline, and may coexist with psoriasis on the elbows, knees, and sacral area, as well as nail changes.

Seborrhoeic dermatitis usually presents with finer, more yellowish or greasy scales, with a characteristic distribution in sebaceous areas. However, there is an intermediate zone called sebopsoriasis, where features of both conditions overlap. That is why, sometimes, looking at a photograph is simply not enough.

How do you tell seborrhoeic dermatitis apart from atopic dermatitis?

Atopic dermatitis is usually associated with significant itching, dry skin, a history of eczema, involvement of other characteristic areas, and a marked impairment of the skin barrier. Seborrhoeic dermatitis, on the other hand, has a predilection for sebum-rich areas.

In some patients both conditions can coexist, and atopic dermatitis itself has a broad differential diagnosis that includes seborrhoeic dermatitis and psoriasis.

How do you tell seborrhoeic dermatitis apart from scalp ringworm?

This distinction is especially important in children. Tinea capitis is a true dermatophyte infection that can cause scaling, itching, broken hairs, patches of alopecia, black dots, and significant inflammation; a severe form can produce a kerion. Unlike seborrhoeic dermatitis, scalp ringworm may require systemic antifungal treatment.

That is why a child presenting with scaling and localised hair loss should not automatically receive a diagnosis of 'dandruff'.

What if I have scales around my nose and eyebrows?

That is a very typical location. Facial seborrhoeic dermatitis frequently appears between the eyebrows, on the eyebrows, in the nasolabial folds, on the sides of the nose, in the beard area, and around the ears, and can cause redness, fine scales, itching, and a sensation of irritation.

It can be confused with rosacea, contact dermatitis, atopic dermatitis, and psoriasis.

Can it be confused with rosacea?

Yes, especially when it affects the nose and the central area of the face. However, rosacea usually presents with other features: flushing, persistent centrofacial erythema, telangiectasias, papules, and pustules.

And both conditions can coexist. That is why a patient may need treatment for seborrhoeic dermatitis and for rosacea at the same time.

Can a shampoo or hair product trigger something similar?

Yes. Contact dermatitis caused by shampoos, dyes, fragrances, preservatives, or styling products can produce itching, redness, and scaling.

If a presumed seborrhoeic dermatitis appears after introducing a new product or does not respond as expected, the diagnosis should be reconsidered.

Are oils good for seborrheic dermatitis?

Here we must avoid universal recommendations. Some oils may temporarily help soften flakes, but applying large amounts of oils chronically to a scalp with seborrheic dermatitis does not necessarily improve the condition. Malassezia is lipophilic, and the goal is not simply to 'grease skin that flakes.'

Flaking does not automatically mean a lack of oil: it can mean inflammation and barrier disruption.

What about natural remedies?

We constantly come across recommendations for vinegar, baking soda, essential oils, lemon, alcohol, tea tree oil, and homemade mixtures. Some of these substances do have interesting biological properties, but 'natural' does not mean 'harmless'.

Essential oils can cause irritation, contact dermatitis, and sensitization, and acids or homemade mixtures can further disrupt the skin barrier. If inflammation is already present, irritating the skin further is rarely a good strategy.

Does diet cause seborrheic dermatitis?

At present, we do not have sufficient evidence to state that there is a universal diet capable of curing seborrheic dermatitis. Metabolic health, nutrition, and the microbiome are fascinating areas of research, but we must avoid turning associations into causation. There is no universal, scientifically validated list of 'forbidden foods for seborrheic dermatitis'.

If a patient reproducibly identifies an individual trigger, we can investigate it. But eliminating gluten, dairy, sugar, yeast, or entire food groups without a specific indication is not part of standard treatment.

Does seborrhoeic dermatitis mean I have candidiasis?

No. Malassezia and Candida are not the same thing. And finding seborrhoeic dermatitis does not mean having 'intestinal fungi,' 'systemic candidiasis,' or a hidden digestive problem.

This type of explanation circulates very widely on social media, but we must separate attractive hypotheses from clinical evidence.

When does a very severe case of seborrhoeic dermatitis warrant a broader evaluation?

Seborrhoeic dermatitis is extremely common and, in the vast majority of patients, does not indicate a serious illness. However, very extensive, very intense, suddenly severe, or treatment-resistant forms — when treatment has been correctly carried out — may justify revisiting the diagnosis and the clinical context.

Seborrhoeic dermatitis can be more severe in certain neurological diseases and in states of immunosuppression, including HIV. This does not mean that a person with dandruff should think 'I have a serious illness': it simply means that context matters.

Why does the treatment sometimes 'stop working'?

Before talking about resistance, we should ask ourselves: is it being used correctly? Is the contact time being respected? Is the treatment being applied to the scalp or only to the hair? Has maintenance been completely abandoned? Is there significant inflammation in addition to Malassezia? Is the diagnosis truly seborrheic dermatitis? Could it be psoriasis, contact dermatitis, or tinea capitis?

Very often the problem is not that 'ketoconazole no longer works,' but rather that the strategy needs to be reviewed.

What does maintenance treatment mean?

Let us imagine that during a flare-up we use a treatment and achieve zero itching, zero inflammation, and almost no flaking. The classic mistake is to abandon everything entirely, wait, have the disease return, and start all over again from scratch.

In patients with frequent relapses, it may be more effective to use certain antifungal treatments intermittently and preventively. Current recommendations place particular emphasis on long-term maintenance to reduce relapses, and the specific regimen must be tailored to the product, the patient, and the frequency of flare-ups.

When should you seek medical advice?

A medical evaluation is advisable when dandruff is very severe, there is significant redness, the itching is considerable, there are crusts or sores, localized hair loss appears, the scalp is painful, pustules are present, the usual treatment is not working, the condition spreads considerably across the face or body, or the diagnosis is not clear.

We should also consider seeking evaluation for a sudden and exceptionally intense onset, especially when other symptoms or relevant medical factors are present.

What, then, is the correct strategy?

First, confirm the diagnosis. Then assess how predominant Malassezia, flaking, and inflammation are. During a flare-up, we may need an antifungal, a keratolytic, an anti-inflammatory, or a combination. And afterwards, maintenance.

In the meantime, we must take care of the skin barrier, the cleansing routine, the products used, and individual triggering factors. Because the goal is not to win a seven-day battle against dandruff, but to manage skin that has a tendency to relapse.