There is an interesting relationship between our microbiome and the presence or absence of skin disease. Malassezia, a fungus, plays an essential role in dandruff development. Malassezia is present on all human scalps as part of the normal microbiome. In many people, there is no flaking of the scalp. It is specific host attributes that determine whether a microorganism can cause disease. One must have a susceptibility component in order to have dandruff. Malassezia secretes an enzyme that digests sebum on the scalp producing oleic acid. People who have an inherent hypersensitivity to oleic acid develop dandruff.
However, not all scalp flaking is due to dandruff. Infections, atopic dermatitis, psoriasis, and other autoimmune diseases can present with flaking. If symptoms do not respond to over the counter shampoos and topical agents commonly used for dandruff, it is recommended that you have a dermatologic evaluation.