Dandruff is caused when the natural cycle of skin renewal is speeded up.

This leads to patches of dead skin forming on the surface of the scalp, which come away into the hair, resulting in the flakes associated with dandruff.

What causes the skin renewal cycle to speed up is not always clear. Possible factors may include:

• seborrhoeic dermatitis – a common condition that causes oily skin; people with seborrhoeic dermatitis can also experience flaking on other parts of the body, such as the eyebrows, side of the nose and anywhere where skin folds together, such as the armpits
• malassezia – a type of fungus that normally lives harmlessly on skin, but if it grows out of control can accelerate new skin production

These are thought to be interlinked. The presence of the fungus on skin may provoke an abnormal response from the immune system (the body’s defence against infection), which can then cause skin to become oily.

In turn, oiliness of the skin may encourage further growth of the fungus, which then triggers symptoms of dandruff.

Other possible risk factors for dandruff include:

• emotional stress
• not washing your hair or, conversely, washing your hair too much – some people can irritate their scalp if they shampoo their hair too often
• using other hair products such as hairspray, hair gel and hair mousse
• very hot or cold climates
• other skin conditions such as psoriasis or eczema – two common skin conditions that can cause skin to become dry, red and flaky
• obesity
• having a weakened immune system, which can be the result of a condition such as HIV or as a side effect of a treatment such as chemotherapy

For reasons that are unclear, people with neurological conditions such as Parkinson’s disease, stroke or severe head injuries often develop both dandruff and seborrhoeic dermatitis.

Dandruff does not usually need to be formally diagnosed because its symptoms are obvious. The characteristic dry, white flakes on your scalp or in your hair are typical of the condition.

Seborrhoeic dermatitis

See your GP if you think you have seborrhoeic dermatitis. They can diagnose the condition by looking at the red rash on your skin. Tests are not usually required.

Ruling out other skin conditions

To confirm a diagnosis of seborrhoeic dermatitis, your GP will examine the redness and colour of the scaling on your scalp.

This will enable your GP to rule out a different skin condition called psoriasis, which causes red, flaky, crusty patches of skin and silvery scales and has similar symptoms to seborrhoeic dermatitis.

If your GP thinks a fungal infection may be present in your scalp (for example, scalp ringworm), a skin sample may be taken and sent to a laboratory for testing.

Dandruff is a common skin condition that causes dry white or grey flakes of dead skin to appear in the scalp or hair.

The flakes are often noticeable if they fall from your scalp on to your shoulders. Your scalp may also feel dry and itchy.

It’s not contagious and doesn’t usually pose a threat to health, but can be unpleasant and embarrassing.

Dandruff can range from mild to severe.

What causes dandruff?

The body continually sheds dead skin cells as new cells are formed. In most cases, this is a gradual process that goes unnoticed.

However, this process can speed up, producing excessive amounts of dead skin cells, which causes dandruff.

It’s not always clear why this happens, but possible causes include seborrhoeic dermatitis (see below), a common skin condition that causes oily skin.

While not directly responsible, certain things can make your dandruff worse, such as:

• overuse of hair products
• emotional stress
• washing your hair too much or too little

Read more about the causes of dandruff.

Seborrhoeic dermatitis

If your dandruff is associated with the skin condition seborrhoeic dermatitis, you may also experience additional symptoms.

These can include scaling and itching of the skin. Areas of the body most commonly affected include:

• the scalp
• the face
• in and around the ears
• the front of the chest and between the shoulder blades
• areas where the skin folds together, such as your armpits, groin and inner thighs

The scaling can range from some mild pink patching to widespread thick crusts of skin.

In some cases the scales can become infected, which can lead to the patches becoming red, painful and discharging pus and fluid.

Severe cases of patching on your scalp can result in some degree of hair loss. However, if there is no scarring, the hair should regrow.

Treating dandruff

The main treatment is anti-dandruff shampoo. There are a number of different types available over the counter from most pharmacists and supermarkets.

These work in different ways, depending on the type, so if one type isn’t effective you may want to try another one.

If treatment fails to clear your flaky scalp after a few weeks, or your scalp is particularly itchy, see your GP. You may need stronger prescription shampoo or a short course of a steroid lotion.

Dandruff usually responds well to treatment, but it’s common for it to reoccur. Some people find they are free from symptoms for a while before having a “flare-up”, where symptoms are particularly bad.

In some cases, you may need to use anti-dandruff shampoo on a regular or semi-regular basis to prevent dandruff returning.

Read more about the treatment of dandruff.

When to see your GP

See your GP if your symptoms show no signs of improvement after using anti-dandruff shampoo for two weeks. You may require stronger prescription treatment.

Your GP can examine your scalp to rule out skin conditions such as seborrhoeic dermatitis or psoriasis, which may also require prescription treatment.

If your GP thinks a fungal infection may be present in your scalp (for example, scalp ringworm), a skin sample may be taken and sent to a laboratory for testing.

Who is affected

Dandruff is a common condition. It is estimated that half of all people will be affected by dandruff at some point in their lives.

Dandruff often occurs after puberty and is most common in people in their early 20s, continuing into middle age.

It has been reported that dandruff is more common in men than women. It is thought to affect all ethnic groups equally.

If you have mild dandruff, the condition can be easy to get rid of. 

You could:

• try washing your hair daily with a mild shampoo until the dandruff clears; shampoos containing tea tree oil are particularly effective
• try not to scratch your scalp when using shampoo; instead, gently massage your scalp without scratching, as this will not damage your hair or scalp
• avoid using hair products such as hairspray and gel until the dandruff clears

Spending time outdoors in the sun can help reduce dandruff. However, make sure you protect yourself with sunscreen with the appropriate sun protection factor (SPF) for your skin type.

Anti-dandruff shampoo

If your dandruff is more severe, you’ll probably need to use an anti-dandruff shampoo. These are available over the counter from most supermarkets and pharmacists.

Some of the most widely used anti-dandruff shampoos include:

• zinc pyrithione – which works by killing the malassezia fungi thought partially responsible for dandruff
• salicylic acid – which helps soften and shed dead skin cells on your scalp (some people experience dryness of their scalp after using salicylic acid; using a conditioner after the shampoo can often help)
• selenium sulfide – this works by slowing production of skin cells while also killing the fungi
• ketoconazole shampoo – which has a powerful antifungal effect
• coal tar shampoo – this again can help slow production of dead skin cells

Not every shampoo is suitable for everyone. For example, selenium sulfide may not be recommended for people with blonde or chemically treated hair, as it can discolour the hair.

As a precaution, the use of certain types of anti-dandruff shampoo may not be recommended if pregnant or breastfeeding. Therefore, it is always important to carefully read the instructions that come with the shampoo.

If in doubt, ask your GP or pharmacist for advice.

Applying the shampoo

It is normally recommended that you apply whatever anti-dandruff shampoo you decide to use daily or every other day. Ketoconazole shampoo is an exception and usually only needs to be applied twice a week.

Once your symptoms improve, you may only need to use the shampoo two or three times a week.

Gently massage the shampoo into your hair. It’s important to leave for at least five minutes to allow it to work.

If one type of shampoo does not prove effective or starts to lose its effectiveness, try another type.

If you do not experience an improvement in symptoms after a few weeks of using a shampoo, contact your GP for advice.

Seborrhoeic dermatitis

If you also develop symptoms of seborrhoeic dermatitis, where you have scaling of skin in other parts of the body, your GP may recommend you use a cream or lotion containing ketoconazole.

If you have a flare-up of symptoms, you may be prescribed a short course of a steroid cream or lotion (topical corticosteroids). These are also used if the condition is itchy.

The long-term use of topical corticosteroids is not usually recommended, as it can lead to side effects such as thinning of the skin. However, they can be used over short periods of time (intermittently) to control the condition.