System for treating a head of hair, including a pipe for circulating a liquid, a device for feeding the pipe with water, at least one source of product, the product (P1) comprising one or more surfactants, a device for injecting product into the pipe to form a treatment solution comprising one or more surfactants in a content ranging from 0.35% to 1.5% by weight of surfactant(s) relative to the total weight of the treatment solution, a dispensing device for delivering the treatment solution onto the head of hair (B) with a flow rate of between 0.5 and 5 L/min, better still between 0.8 and 3 L/min.