The flakes are called scale or scales. It can be fine scale (like winter-dried skin or "ashiness") or coarse scale (as with psoriasis).
Psoriasis
The medical term for the abnormal condition of dry and scaly skin is xeroderma. This condition can be caused by various factors such as dry air, skin conditions like eczema, or certain medications. Treatment typically involves applying moisturizers and avoiding triggers that worsen the dryness.
xeroderma
Xeroderma is a condition of Xero = dry + derma = skin. It is a common complaint of winter weather with the scalp, lower legs, arms, knuckles, sides of abdomen and thighs being most affected. The adjective form is "xerodermic" (-ic = pertaining to).
Dermoid is the medical term meaning skin-like
The medical term for "pertaining to scales or covered with scales" is "squamous." This term is commonly used to describe certain types of epithelial cells or skin conditions characterized by scale-like appearance.
Pyoderma is the medical term meaning any purulent skin condition.
Hyperpigmentation is the medical term meaning excessively darkened skin.
Acrochordon is the medical term meaning skin tag. Skin tags can occur in areas of high friction.
Dermatomycosis is the medical term meaning fungal disease of the skin.
The medical term meaning Tb skin test is Mantoux. It's a term that refers to a skin test to check for tuburculosis.
"Sub-" is the prefix in the medical term that means below the skin.
Hyperpigmentation is the medical term meaning excessively darkened skin.