Dead skin cells and oil (plus other debris) form a plug inside the pore. If this plug does not become inflamed, it can become a whitehead — a non-inflamed lesion under the skin, also called a “closed comedone”. This is also called “maturation arrest” acne, as it has not “matured” into a blackhead yet.

CLOSED COMEDONE

This is another non-inflamed acne lesion called a blackhead, where the pore remains open, also known as an “open comedone.”  In the case of a blackhead, the tip of the plug darkens as it is exposed to oxygen in the environment.

OPEN COMEDONE

As the oil and the dead skin cells build up, they put pressure on the cells surrounding the pore. With enough pressure, the sides of the pore rupture and the contents of the pore leak into the surrounding skin.  Because this material contains a lot of P. acnes bacteria, the surrounding skin now becomes infected, creating a red bump that we know as a pimple. The medical term for this red bump is an inflammatory papule.

INFLAMMATORY PAPULE

This is a pustule which is different from a pimple only in that it contains white blood cells. When the immune system fights off the P. acnes infection, white blood cells, which are soldiers of the immune system — pile up, creating pus in the pore.

PUSTULE

A nodule is a solid dome-shaped lesion that extends below the surface, deep into the layers of the skin. Scarring is common with nodules and can sometimes leave an impaction behind, which can flare again and again.

NODULE

When a group of pustules cluster together under the skin, they form a cyst. An acne cyst can appear similar to a nodule, but is pus-filled, and can have a diameter of 5mm or more across. They are usually very painful and scarring is common with cysts.

PUSTULES CLUSTER