Pustules are small, slightly elevated, red, sore bumps with a white or yellow pus-filled center, commonly found on the face, neck, back, chest, shoulders, and upper arms. They are more commonly known as “pimples” or “zits.”
After a couple of days on the skin, a pustule will release its pus and begin the healing process. Most pustules do not leave scars.
Around 85% of all individuals between the ages of 12 and 24 years will develop acne, and as pustules are a common type of acne lesion, it is likely that a similar percentage of people will develop one or more pustules during these ages.1
How Pustules Develop
Pustules develop in four steps.
- Blockage of a hair follicle. Acne development begins with microscopic hair follicles (pores) in the skin. Attached to these pores are glands called sebaceous glands, which produce sebum (skin oil). Normally, the sebum flows freely from the pore and onto the surface of the skin. Acne develops when the opening of a pore becomes blocked with dead skin cells, and this blockage results in sebum buildup inside the pore. Although scientists do not completely understand what causes this blockage, it is thought that inflammation, androgens (male hormones found in both males and females), and excessive sebum production play a role.
- Formation of a comedone. After the pore is blocked and sebum begins to build up inside the pore, it becomes larger and visible. The visible sebum-filled pore is called a comedone, which is more commonly known as a whitehead or blackhead.2,3
- Growth of P. acnes and papule formation. Inside of a comedone, there is a buildup of sebum—and because the pore is blocked, there is also little to no oxygen inside the pore. This is the ideal environment for a kind of skin bacteria called Propionibacterium acnes (P. acnes). P. acnes feeds on the sebum and begins to reproduce rapidly. Small amounts of this bacteria are found in all people's skin pores, but as the quantity increases inside a blocked pore, the body views it as an infection and responds by sending in inflammatory cells called neutrophils to fight the infection. Neutrophils release enzymes that attack P. acnes in order to clear it from the clogged pore. This can weaken the wall of the pore, and eventually cause the pore to rupture. When the pore ruptures, the pore’s contents (sebum, P. acnes, neutrophils, and dead skin cells) are released into the surrounding skin. The body views these contents as “invaders” and responds with an inflammatory response that creates an inflamed, red, firm, slightly raised and sore acne lesion called a papule.4–6
- Formation of a pustule. Normally, a papule fills with pus. At that point it becomes a pustule, which is softer than a papule. The pus that eventually fills the lesion is the result of the “battle” between P. acnes and the neutrophils, both of which are killed during the battle, and the result of this death is pus. Pus is a white or yellow liquid that is made of dead neutrophils (white blood cells), along with serum (protein-rich liquid). The white blood cells give pus its characteristic color.6,7
How Long Do Pustules Remain on the Skin?
Once an acne lesion has developed into a pustule, it can remain on the skin for several days. Researchers have found that how a pustule develops can determine how long it will last.
A 1974 study published in the Journal of Investigative Dermatology found that pustules developing from blackheads remained on the skin for an average of 5.2 days, while pustules developing from whiteheads remained on the skin for an average of 8.2 days. After this time, the head of the pustule with either break spontaneously, or it will break through picking or popping the lesion. Once the head of the pustule breaks, the lesion releases the pus and other contents of the pore onto the surface of the skin. The lesion then heals, usually with minimal scarring.8,9