Nioxin Diaboost (marketed as Diamax Advanced in some regions) is a leave-in scalp serum formulated to increase the diameter of individual hair strands, so fine or thinning hair looks denser without a rinse-out step.
The formula centers on niacinamide and caffeine, paired with cooling wild mint and peppermint oils, and Nioxin describes it as boosting hair diameter while helping protect strands against breakage. Because the active ingredients are meant to work at the root, it's applied directly to the scalp rather than smoothed through the lengths the way a leave-in conditioner would be — a small amount is massaged into the scalp with the fingertips and left in, and hair is then styled as usual.
It's positioned as a daily habit rather than a one-time fix, layered underneath regular styling products, and Nioxin states it's suitable for all hair types, including color-treated hair.
It's worth noting this is a cosmetic strand-thickening serum that changes how existing hair looks and behaves — it isn't a hair-growth drug and doesn't claim to stimulate new growth.
