Causes Of Dandruff. Skin cells are formed continuously on the scalp,  so the shedding of dead skin cells is a normal process. Sometimes with dandruff, however, skin cells are shed at a faster rate than normal. Oil from the scalp causes the skin cells to clump together and appear as white flakes. Dandruff can be caused by a number of things, including dry skin; sensitivity to hair products; and skin conditions such as seborrheic dermatitis or eczema. The overgrowth of a yeast-like fungus can also cause dandruff. This overgrowth can be caused by stress, hormones, too much oil on the scalp, or problems with the immune system.