What does sheen mean in hair?

In hair care and beauty, sheen means a soft, healthy, luminous shine or glow on the hair that indicates smoothness, moisture, and overall hair health. When hair has sheen, it reflects light evenly because the cuticle layer, the outermost protective layer of each strand, is smooth, flat, and intact, allowing light to bounce off rather than being scattered by rough or damaged areas. Hair with good sheen looks glossy, silky, and vibrant, while hair that lacks sheen looks dull, dry, frizzy, or lackluster due to damage, dehydration, or product buildup. Sheen is different from an oily or greasy shine. A natural sheen is desirable and suggests well-moisturized, well-conditioned hair, whereas excessive greasiness looks oily. Many hair products are designed to enhance sheen, including hair glosses, glazes, serums, oils, and leave-in conditioners that smooth the cuticle. In textured and Black hair care, sheen is often used to describe a soft glow as opposed to a high-gloss shine, and products are marketed to add sheen without heavy grease. So in hair, sheen is essentially a sign of health and polish.