What’s the difference between dry scalp and dandruff? There’s a common misconception that if you have dandruff, your scalp must be dry—when really, these are two different diagnoses, according to Pooja Rambhia, MD, a board-certified dermatologist at Union Derm. Scalp psoriasis and scalp eczema are other common skin disorders that cause skin cells to grow extremely fast and become patches of dry, itchy, flaky skin, according to Dr. Robinson.