Oily skin is mainly due to hormonal factors. The activity of the sebaceous glands is hormone-dependent. We know that an increase in androgynous hormones during adolescence, in both boys and girls, stimulates sebum (oil) production by a significant amount. This changes the condition of the skin, which goes from a normal condition to an oily or combination skin type. In women, another hormone, LH, increases just after ovulation, causing excessive sebum production at the end of the menstrual cycle, just before the period. There are also other factors:

• Age: sebum secretion is very high at birth, low in the pre-pubescent period, and at its peak between 15 and 30 years of age. It drops significantly after 50.
• The time of day: sebum secretion is at its peak in the early morning, low in the evening and in the middle of the night - another effect of hormonal fluctuations.
• Nervous state: stress and anxiety can stimulate sebaceous activity.
• Finally, 'environmental' factors: an increase in heat and humidity can increase hyper-seborrhea. Air quality also plays an essential role. In a polluted or smoky environment, micro-particles (heavy metals, cigarette tar) are deposited on the skin and obstruct the pores.