Pimples, blackheads, and other forms of acne don’t just pop up anywhere — they come from specific sites on the skin, called pilosebaceous units.2 These little structures just below the skin are where the hairs grow, and where sebum, a natural skin oil, is produced. Picture them a bit like an old stone well in the ground, where the stones of the inner wall are specialised skin cells (follicular keratinocytes), and the sebum seeps in from small tunnels in the sides (via oil glands). The hair itself grows up the middle and extends above the ground.
When things work properly, skin cells (the stones in our analogy) are gradually shed and pushed up the follicle with the flow of sebum, where they’re cleared through the surface of the skin.2 If there’s a blockage in the well, acne is the result.
You might think that blockages typically come from the outside, like dirt or grime on the skin — debris that can fall in and clog up the well — but that’s not really the case. True, there are some cosmetic ingredients or products that are ‘comedogenic’, meaning they interfere with the normal processes of cell shedding and sebum flow, making blockages more likely,3 but acne is a condition that begins inside the skin.
If there is too much sebum produced, or the cells along the wall of the follicle aren’t shed cleanly or quickly enough, they can stick together and form a plug in the shaft. More sebum builds up behind the plug, which makes an attractive meal for the bacteria Cutibacterium acnes. As the bacteria eats the extra sebum, it releases waste products that worsen inflammation.2 Picture this as a partial cave-in of stones in the well, causing muddy water to build up underneath.
