Dandruff
The exact cause of dandruff is unknown, but it is not linked to poor hygiene.
Possible causes of dandruff include:
- a reaction to a type of yeast that lives on the skin called a Malassezia
- hormones, which may be involved because dandruff commonly occurs after puberty
- not brushing your hair regularly, which may lead to dandruff because the dead skin cells are not able to shed properly
- a fungal infection, either of the outer layers of the skin (superficial fungal infection) or the deeper layers of the skin (subcutaneous fungal infection) caused by fungi such as moulds and yeasts
- stress, which is also thought to trigger dandruff or make the symptoms worse
People with dry skin are more likely to be affected by dandruff.
If you have dandruff, your symptoms may improve during warmer months and get worse when it is colder. This is because the ultraviolet (UV) light from the sun is thought to counteract (act against) the yeast on your skin.
Seborrhoeic dermatitis
The cause of seborrhoeic dermatitis is not fully understood. However, it is believed to be caused by the following:
- a reaction to a type of yeast living on the skin called a Malassezia
- genetics (the condition appears to run in families)
- the production of too much oil on the skin
Seborrhoeic dermatitis is also more likely to occur in people with the following conditions:
- Parkinson’s disease: a chronic (long-term) neurological condition that is caused by a loss of nerve cells in the brain
- stroke: a serious medical condition that occurs when the blood supply to the brain is disturbed
- HIV: a long-term (chronic) virus that attacks the body’s immune system
Seborrhoeic dermatitis is more common in people with these conditions because the yeasts that are thought to cause the condition (Malassezia yeasts) grow more easily in people who are immunocompromised (have a weakened immune system) and those with certain neurological conditions (which affect the nervous system).
Other factors
Other factors that may increase your risk of developing seborrhoeic dermatitis include:
- an illness that reduces general health
- psychological stress
- fatigue (tiredness)
- change of season
- some medicines (these may induce or make seborrhoeic dermatitis flare up)
