Dry skin - Dandruff can develop as a result of your scalp's skin flaking and itching due to dry skin.
Fungus - Dandruff can be brought on by an overabundance of the yeast-like fungus Malassezia on the scalp.
Seborrheic dermatitis - A type of eczema that may lead to sebaceous glands overproducing scalp sebum, leading to itchy, inflamed and oily scalp. In many cases, seborrheic dermatitis is the root of dandruff.
Not shampooing enough - Dandruff can develop as a result of an accumulation of oil and dead skin cells on the scalp due to insufficient shampooing.
Certain hair products might irritate the scalp and cause dandruff if they contain strong chemicals or smells.