Sebum is a natural component found on the scalp. It is a film that protects against external aggressors. When there is a balanced amount of it, our hair is radiant and full of life. But under the effect of certain factors such as stress, pollution, a hormonal imbalance, inadequate care, etc., the sebaceous glands begin to produce an excess of sebum that suffocates the roots and weighs the hair down. The hair then becomes oily and tends to become greasy more quickly after each wash.