Papules are relatively small, slightly elevated, red, sore bumps less than 5mm in diameter that are commonly found on the face, neck, back, chest, shoulders, and upper arms. Papules do not contain a white or yellow center because they have not yet filled with pus, and this lack of pus is what makes them different from pustules. Around 85% of all individuals between the ages of 12 and 24 will develop acne, and because papules are a common type of acne lesion, it is likely that the same percentage of people will also develop at least one papule.1
How Papules Develop
Most papules are formed in three 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 freely flows out of the pore and onto the surface of the skin. Acne develops when a pore becomes blocked with skin cells, and this blockage causes the sebum to accumulate inside the pore. Although scientists do not know what causes this blockage, it is thought that inflammation, androgens (hormones), and excessive sebum production play a role.
- Formation of a comedone. Once the pore is blocked and sebum begins accumulating inside the pore, it enlarges and becomes visible. This visible acne lesion is called a comedone, which is more commonly known as a whitehead or blackhead.
Growth of P. acnes and the formation of a papule. Inside of a comedone is a large accumulation of sebum, but because the pore is blocked, there is little to no oxygen. This is a suitable environment for a type of skin bacteria called Propionibacterium acnes (P. acnes). Inside the comedone, P. acnes feeds on the sebum and begins to reproduce rapidly. Small numbers of this bacteria are expected in every human's skin pores, but as the amount of P. acnes present inside the pore increases, the body sees it as an infection and responds by sending in inflammatory cells called neutrophils. Neutrophils release enzymes to attack the P. acnes in order to kill it. However, this weakens the wall of the pore, and can cause the pore to rupture. This rupture ends up releasing the contents of the pore (sebum, P. acnes, neutrophils, and dead skin cells) into the surrounding skin. The body views these contents as “invaders” and responds with an inflammatory response, resulting in an inflamed, red, firm, slightly raised and sore acne lesion called a papule.2–4
Another way papules develop. Research has found that most papules develop from the way we have just discussed; blockage of a pore, the formation of a comedone, and the growth of P. acnes.
However, a 2008 study published in the Journal of the American Academy of Dermatology found that step two of papule development was skipped in 28% of acne patients. That is to say, they had papules that did not develop from a whitehead or blackhead. Instead, the papules developed directly from an initial clogged pore.
Researchers do not yet fully understand how this happens.5
How Long Do Papules Remain on the Skin?
Once an acne lesion has developed into a papule, it remains for a few days. After this time, nearly all papules fill with pus and become pustules, which are the acne lesions that people normally refer to as "zits" that have a white/yellow center and can be popped.
Occasionally, papules sometimes stay on the skin for multiple days or even weeks without developing into pustules, but this is rare. How a papule develops can determine how long it will remain on the skin.
A 1974 study published in the Journal of Investigative Dermatology found that papules developing from whiteheads remained on the skin for an average of 4.9 days, while papules developing from blackheads remained on the skin for an average of 8.6 days. After these time periods the papules then developed into pustules.
Researchers have not studied how long papules remain on the skin when they develop directly from initial clogged pores. Generally, whiteheads, blackheads, papules, and pustules clear and leave minimal scarring.6,7
Never Pop a Papule!
Because papules are not filled with pus, they cannot be popped. If you attempt to pop a papule, it will likely make the lesion worse, cause it to stay around for a longer time, and increase the chance of scarring. Always wait until a papule has filled with pus and has an obvious white or yellow center before attempting to pop it.