When follicles are blocked by sebum, debris and dead skin cells, the follicular wall experiences pressure. If the pressure is great enough, the follicle wall will break and the contents will spread into the surrounding skin.
When your immune system responds to this bacteria and sebum, inflamed blemishes present. The degree of inflammation determines the size and severity of the blemish.
Papules: Pink or red bumps without a white or yellow centre (pus).
Pustules: Red bumps with a white or yellow centre, indicating the presence of pus. Pustules are formed when the plug inside a pore traps oil and bacteria, which draws white blood cells to the area to fight infection. Pus is made up of dead white blood cells.
Cysts and nodules: Larger (and often painful) lesions that extend into the deeper skin layers. Cysts and nodules can last for months, destroy the follicle and lead to permanent scars. Individuals with this type of acne should see a dermatologist for treatment.