Dandruff occurs, essentially, when small bits of dry skin are shed from the scalp. You might spy these flakes in your hair or on your shoulders. Dandruff may make your scalp itchy, too. It’s a common problem, but it isn’t as simple as it seems. Dandruff is actually quite tricky to define because it overlaps with seborrheic dermatitis (a chronic form of eczema) and other skin conditions that lead to a scaly scalp.