Acne is essentially caused by the hair follicles in the skin becoming blocked.
The sebaceous glands beneath the surface of the skin are attached to these follicles in order to lubricate the hair and skin with the sebum they produce.
Acne occurs when these glands produce too much sebum which mixes with dead skin cells and they plug the follicle.
This makes the follicle bulge outwards, creating a whitehead. Or it can be open to the skin, creating a blackhead.
These plugged follicles can then become infected by the bacteria that lives on the skin, which leads to papules, pustules, nodules or cysts.2
There are other contributing factors to acne, including certain medications, smoking or regularly wearing items such as headbands, that place pressure on an area of skin.