By using its pigmentation, the optical density can be improved in dark-haired individuals. It is not ideal for blonde or gray hair.
It is only possible for people with thin hair (male / female) or for people with a hair transplant.
By making the scalp darker, there will be less contrast between the hair color and the skin color.
This will create the illusion of a fuller head of hair.
5-10 years, then a refreshment or touch up is required.