Flaky, itchy skin on the scalp is one of the most common reasons people visit a pharmacy, and it usually falls into one of two closely related conditions: dandruff or seborrhoeic dermatitis. They sit on the same spectrum, share the same underlying trigger, and are managed with much the same treatments, but knowing which one you have (and what else it might be mistaken for) helps you pick the right first step.
This guide explains what actually causes dandruff and seborrhoeic dermatitis, how to tell them apart from scalp psoriasis, the shampoos and treatments that work, and when it is worth asking a pharmacist or doctor for something stronger.
Both conditions are very common, tend to run a long-term, up-and-down course, and can affect adults of any age, although they are often more noticeable in oily skin types and in colder months. Neither is contagious, and having dandruff or seborrhoeic dermatitis says nothing about how clean you keep your hair or skin.
What causes dandruff and seborrhoeic dermatitis
A yeast called Malassezia lives naturally on the skin of almost everyone, feeding on the oils produced by hair follicles. In most people it causes no trouble at all. In some, though, it overgrows or provokes an inflammatory reaction in the skin, and it is this reaction, rather than the yeast itself, that causes the flaking, itching and redness of dandruff and seborrhoeic dermatitis. Because Malassezia thrives on oily skin, both conditions tend to affect areas with more active oil glands: the scalp, eyebrows, sides of the nose, ears and chest.
Dandruff is generally considered the mildest end of this spectrum, limited to flaking and itching of the scalp without much visible redness. Seborrhoeic dermatitis describes a more inflamed version of the same process, with greasy, yellowish scale, redness, and a tendency to spread beyond the scalp to the face and upper body. A number of things can tip the balance towards a flare, including naturally oily skin, cold and dry weather, stress, tiredness, and a weakened immune system. It is not caused by poor hygiene, and over-washing can sometimes make things worse by irritating an already sensitive scalp.
Dandruff, seborrhoeic dermatitis or scalp psoriasis: telling them apart
These three conditions can look similar at first glance, but there are useful clues. Plain dandruff produces fine, white or grey flakes with an itchy scalp but little or no redness underneath. Seborrhoeic dermatitis tends to produce greasier, yellowish scale sitting on visibly red or inflamed skin, and it often extends past the hairline to the eyebrows, the creases beside the nose, behind the ears or onto the chest. In babies, the same process causes cradle cap, which usually clears on its own within the first few months of life.
Scalp psoriasis, by contrast, tends to form thicker, more sharply defined patches with a silvery-white scale, and the patches can extend well beyond the hairline onto the forehead or neck. People with scalp psoriasis often have, or go on to develop, patches elsewhere too, such as the elbows, knees or nails. The two conditions can overlap, and some people have features of both, so if the picture is not clear cut, or treatment is not helping, it is worth having it assessed by a pharmacist or GP rather than guessing.
First-line treatment: medicated shampoos
For most people, a medicated shampoo is the starting point, and it is often all that is needed. Ketoconazole shampoo is the best-known option, available both over the counter and on prescription, and it works by reducing the Malassezia yeast on the scalp. It is usually massaged into wet hair, left on for around five minutes to give it time to work, then rinsed off, using it two to three times a week during a flare.
Other medicated shampoos use different active ingredients to similar effect, including selenium sulfide, zinc pyrithione, coal tar and ciclopirox. It typically takes two to four weeks of regular use to see the full benefit, and treatment is usually continued for a few days after the flaking and itching have settled, then stepped down to a lower frequency, such as once a week or fortnightly, to keep symptoms under control long term. If you have a beard or facial hair affected by the same process, the same medicated shampoo can usually be used as a wash for those areas too.
A common mistake is rinsing the shampoo off too quickly, before it has had time to work, or switching to a different product after only a few days because there has been no obvious improvement yet. Giving one product a proper trial of two to four weeks, used consistently at the recommended frequency, gives a much clearer picture of whether it is working than chopping and changing between different shampoos. It also helps to use a normal, gentle shampoo on the days in between, rather than the medicated one daily, since more frequent use is not necessarily more effective and can be drying.
Prescription options when shampoos are not enough
When a medicated shampoo alone does not settle things, or the scalp is particularly inflamed, a pharmacist or GP can prescribe something stronger. For the scalp specifically, this often means a topical corticosteroid scalp application, sometimes combined with an ingredient that helps loosen thick scale, such as Diprosalic (betamethasone with salicylic acid), or a corticosteroid scalp application on its own, such as Betacap. These are usually used for a short, defined course to bring inflammation under control, rather than continuously.
Topical steroids are effective but are not meant for indefinite daily use, particularly on thinner skin, because prolonged use can lead to skin thinning and other side effects. A clinician will typically advise a course of no more than a few weeks, stepping back to a medicated shampoo alone once things have settled, and reviewing with you if a flare keeps returning quickly.
Seborrhoeic dermatitis on the face and other areas
Seborrhoeic dermatitis often extends beyond the scalp, commonly affecting the eyebrows, the creases beside the nose, the ears and, less often, the eyelid margins and the chest. Facial skin is thinner and more sensitive than the scalp, so treatment is usually gentler: a short course of a mild topical corticosteroid such as hydrocortisone 1% cream, or an antifungal cream applied directly to affected areas, in place of a shampoo left on the skin.
Alongside any prescribed treatment, simple skincare choices help keep facial seborrhoeic dermatitis calmer between flares: a gentle, non-foaming cleanser, a light, non-greasy moisturiser, and avoiding heavy, oily or highly fragranced skincare products that can feed the same process they are meant to soothe. On the chest and back, the medicated shampoos used for the scalp can usually be applied as a wash in the shower in the same way.
When to see a doctor or pharmacist
Most cases of dandruff and mild seborrhoeic dermatitis can be managed with an over-the-counter medicated shampoo, so it is reasonable to try one for a few weeks before seeking further help. It is worth speaking to a pharmacist or GP if symptoms do not improve despite regular use, if the affected area is widespread or spreading, if the skin becomes very red, weeping or painful, or if the eyes are involved, since eyelid margin involvement needs its own careful assessment.
It is also sensible to get a proper diagnosis if you are not sure whether you are dealing with dandruff, seborrhoeic dermatitis or something else, such as scalp psoriasis or a different skin condition, since the right treatment depends on getting that right. Seborrhoeic dermatitis that is unusually severe or resistant to treatment can occasionally be linked to another underlying health condition, so a clinician may want to consider your wider health picture as part of the assessment.
Seek advice sooner rather than later if the skin looks infected, for example if it becomes increasingly painful, swollen, or starts weeping or crusting with pus, or if you feel generally unwell alongside the rash, since these are signs that need proper assessment rather than home management. Most people, though, find that a straightforward combination of a medicated shampoo and, where needed, a short prescribed course for more stubborn patches keeps dandruff and seborrhoeic dermatitis well controlled long term.