Dandruff (pityriasis capitis) is a chronic, non-inflammatory condition characterised by excessive shedding of the cornified cells of the scalp in the form of scales, sometimes accompanied by itching and redness. It is caused by increased production of horny substance and cell turnover on the scalp and may be associated with raised androgen levels.

Also, sufferers have higher levels of microorganisms – particularly the yeast Pityrosporum ovale – on the scalp. It has not been proven whether this organism is the cause of dandruff, but antimicrobial shampoos appear to control the condition.

Seborrhoea (seborrhoeic dermatitis) is the result of accelerated epidermal proliferation and sebaceous gland activity on the scalp, face and trunk. On the scalp, the condition may be difficult to distinguish from more severe forms of dandruff, as characteristic features are the presence of greasy scales and often pruritus. As in dandruff, growth of P. ovale is increased in the scaly epidermis and may be a causative agent.