Our dermatologist's opinion
The sebaceous glands produce sebum, a fatty substance indispensable to correct skin balance. Certain areas of the body have more sebaceous glands, particularly the T zone of the face (forehead, nose, chin), the back and the torso.
During an acne outbreak or in greasier skins, sebum is manufactured to excess. The skin becomes greasy and sometimes shiny. Pores on the nose are dilated and blackheads appear, the result of oxidation of the sebum at the pore's surface.
Blocking of the skin's pores by sebum can sometimes be complicated by a local inflammation from multiplication of a common skin germ called Propionibacterium acnes or P.acnes. This results in red or white spots on the areas where sebum is produced (T zone, back, torso).


The advice of Didier Rase
In order to avoid these little unattractive inconveniences, I would advise that you cleanse your skin regularly using an exfoliation mask then apply a moisturiser every day. You must avoid over-greasy creams and above all hygiene products that are too aggressive, thus stimulating sebum production.