Excess production of sebum, the natural oil secreted from glands in the skin, fuels the growth of the fungus. This helps to explain why dandruff often starts in puberty when hormone changes occur and why people with oily scalps suffer more. Dandruff is also believed to run in families. Diets that are too salty, spicy, sugary, and accompanied by too much alcohol make it worse. So can stress and changes in climate.
Seborrhoeic eczema causes itchy and flaky patches on the scalp.
This tends to be more severe than simple dandruff because the skin and glands become inflamed. Self-help tips experiment to find out how often your hair needs washing. It's usually trial and error finding the one that works for you. For more stubborn dandruff or seborrhoeic eczema using selenium, zinc, coal tar in coconut oil, or salicylic acid can be successful. Scalp preparations contain various combinations of these or all of them together.