What is the white fungus on hair?

The white fungus on hair is likely to be dandruff, also known as pityriasis capitis, which is a common scalp condition that causes the skin on the scalp to flake. It is caused by an overgrowth of a type of fungus called Malassezia, which lives on the scalp and feeds on the oils produced by the sebaceous glands. As the fungus breaks down these oils, it produces a substance that irritates the scalp, causing itching and flaking. Other factors such as dry skin, poor hygiene and stress can also contribute to dandruff.