All acne starts with a hair follicle. Each hair follicle is made up of three main components: A follicle shaft, a hair and an oil producing gland, known as the sebaceous gland.
The skin cells that line the follicle shaft are replaced by new ones every twenty-eight days. In acne, the cells lining the follicle wall produce too much keratin (a substance that helps to protect the skin from damage). This excess of keratin can cause the dead skin cells to stick together, making them harder to expel.
Cells that are not expelled mix with the flow of oil that is produced by the sebaceous gland and can form a blockage in the hair follicle. This plug of cells and oil is how most acne begins. Although, sometimes the blockage can come from outside of the hair follicle, when substances (such as make-up, sweat and oil on the skin’s surface) enter into the follicle’s opening and become trapped.
These early blockages are known as microcomedones and are too small to be seen with the eye.
When oil, dead skin cells and other debris continue to add to a blockage in a hair follicle then the blockage will grow and become visible.
If this larger blockage is located near the surface of the hair follicle it will breach the follicle opening, known as a pore, and protrude out onto the surface of the skin. Oxygen in the air will then react with pigment in the oil, causing the blockage to turn a dark colour (the dark colour is not caused by dirt and cannot be washed away). This type of blockage is known as a blackhead.
When oil, dead skin cells and other debris continue to add to a blockage in a hair follicle then the blockage will grow and become visible.
If this larger blockage is located deeper down in the hair follicle it will force the opening of the hair follicle, known as a pore, to close around it. This is known as a whitehead.
The term whitehead is often misused to refer to an acne lesion known as a pustule. In actual whiteheads, there is no inflammation or pus.
A form of acne known as ‘solar comedones’ can form on areas of skin that have received relatively high levels of exposure to the sun, such as the cheeks. This type of acne often appears only in the middle-aged and elderly and can be made up of whiteheads, blackheads or a combination of both.
Papules form when bacteria multiply within a blocked hair follicle. As oil, dead skin cells and other debris continue to add to a blockage and make it grow larger there is a risk that the blockage will tear open the follicle wall. Follicle walls can also tear as a result of picking at or trying to squeeze out a whitehead or a blackhead.
When a follicle wall tears, white blood cells rush in to fight the bacteria, causing inflammation. The white blood cells then cluster and form a pocket of pus within the affected hair follicle. This is known as a papule.
Pustules normally form a few days after a papule as the pocket of pus rises to the surface of the inflammation. Pustules are often, mistakenly, referred to as whiteheads.
Acne nodules and cysts are generic terms that are used to refer to particularly large papules or pustules.
When the follicle wall surrounding a blocked hair follicle splits, or splits further, the contents of the blockage (along with its bacteria) can spill out into the surrounding tissue. White blood cells then rush in and cause inflammation in the wider area. This type of lesion is also generally known as an acne nodule.
When the inflamed area becomes filled with pus, it is then generally referred to as an acne cyst.
Acne nodules and acne cysts can take a long time to heal if left untreated. If you think that you might have an acne nodule or cyst then it is advised that you see your doctor, who can inform you of the best treatment options.
Acne can occur as a single spot or as a variety of the lesions described on this page spread over an area of skin. When a person has multiple lesions, be it the same type of lesion or a mixture of types, spread over an area of skin it is known as acne vulgaris (with the vulgaris meaning ‘common’).