First, toughness: the hair is strong, elastic and without bifurcation. A healthy hair can lift about100g, and its toughness is equivalent to a metal wire with the same thickness. The toughness and elasticity of injured hair will be greatly reduced, and it is easy to break hair and split hair.
Second, moist: moist, not greasy, no static electricity. Healthy hair retains about 10% moisture in a mild environment, and only absorbs about 15% moisture of its own weight even if it is completely wet. The injured hair loses water seriously when it is dry, causing problems such as dryness, static electricity and flying hair. But when it is completely wet, it will absorb too much water, up to 200% of its own weight.
Third, soft: soft and smooth, easy to comb, not knotted. Healthy hair feels like satin, soft but not astringent, smooth but not greasy, and easy to set. Injured hair feels as dry as branches, easy to knot and difficult to set.
Fourth, bright: shiny, full of hair color, bright. Healthy hair is solid and full in color, and injured hair is frivolous and dim as straw.