Skin abscesses are caused by bacteria entering the skin through a break, cut, or blocked hair follicle. The overwhelming majority are caused by Staphylococcus aureus, a bacterium that lives harmlessly on many people’s skin until it finds a way beneath the surface. Once inside, your immune system floods the area with white blood cells to fight the infection, and the battle between bacteria and immune cells produces pus, a thick mixture of living and dead white blood cells, dead tissue, and germs. That pus collects in a walled-off pocket, forming the painful, swollen lump you can see and feel.
How Bacteria Get Through the Skin
Your outer layer of skin cells acts as a barrier, but S. aureus has evolved tools to break through it. The bacterium produces a toxin that triggers skin cells to self-destruct in a rapid, inflammatory form of cell death. As those cells die, gaps open in the barrier, letting bacteria pass through to the tissue underneath. This process also releases inflammatory signals that attract more immune cells to the site, which is why an abscess becomes red, hot, and swollen so quickly.
The most common entry points are damaged hair follicles. Shaving, waxing, tight clothing, and friction from skin rubbing against skin can all injure follicles enough to let bacteria in. When an infected follicle becomes deeply inflamed, it forms a boil (also called a furuncle). If several neighboring boils connect beneath the skin, they create a larger, deeper infection called a carbuncle, which tends to cause more scarring. Boils most often appear on the neck, face, breasts, buttocks, and armpits, all areas with friction and sweat.
The Role of MRSA
Not all staph bacteria respond to standard antibiotics. A strain called MRSA (methicillin-resistant Staphylococcus aureus) has become one of the most common causes of skin infections seen in emergency departments. In one recent study of complicated skin and soft tissue infections, S. aureus accounted for over 60% of all bacteria identified, and about a quarter of those were confirmed as MRSA.
What makes MRSA significant for you is that it used to be found mainly in hospitals but now spreads easily in the community, through shared gym equipment, towels, and close physical contact. An abscess caused by MRSA looks and feels the same as any other, but it may not respond to the first antibiotic a doctor prescribes, which is one reason drainage of the abscess itself is the primary treatment rather than pills alone.
Blocked Glands and Hair Follicles
Sometimes abscesses start without an obvious wound. Blocked oil glands or clogged hair follicles can trap bacteria beneath the skin surface, creating a warm, enclosed environment where infection thrives. This is common in areas with dense hair follicles or where sweat and oil accumulate.
A condition called hidradenitis suppurativa causes recurring abscesses in skin folds, particularly the armpits, groin, buttocks, and under the breasts. It develops when hair follicles become blocked repeatedly, though the exact trigger isn’t fully understood. Hormones, genetics, smoking, and excess weight all appear to play a role. People with this condition often deal with painful lumps that drain, heal, and then return in the same areas, sometimes leaving tunnels of scar tissue under the skin.
Risk Factors That Make Abscesses More Likely
Anything that weakens your immune system or damages your skin barrier raises the odds of developing an abscess. Diabetes is one of the most important risk factors. High blood sugar creates an environment where staph bacteria thrive, and people with diabetes get bacterial skin infections significantly more often than people without it. These infections tend to involve the same culprit: staphylococcus colonizing hair follicles and surrounding tissue.
Other factors that increase your risk include:
- Close contact with someone carrying staph or MRSA, especially in households, sports teams, or shared living spaces
- Skin conditions like eczema, which compromise the skin barrier and create entry points for bacteria
- Obesity, which creates more skin folds where moisture and friction encourage bacterial growth
- IV drug use, which introduces bacteria directly beneath the skin
- Immune-suppressing medications or conditions, including chemotherapy, HIV, or long-term steroid use
People who have had one abscess are more likely to get another. Staph bacteria can colonize your nostrils and skin for months, reseeding infections even after the original abscess heals.
Abscesses Without Infection
Not every abscess is caused by bacteria. Sterile abscesses can form when the body reacts to a foreign substance, like an injected medication, a surgical material, or a splinter. The immune system treats the foreign object as a threat and mounts an inflammatory response that produces a pus-like collection, even though no bacteria are involved. These are less common but can look identical to an infected abscess on the surface.
How a Small Infection Becomes a Bigger Problem
Most skin abscesses stay contained. Your body walls off the infection with a fibrous capsule, which is actually why antibiotics alone often can’t reach the bacteria inside. The standard treatment is incision and drainage, where a clinician opens the abscess, lets the pus drain, and may pack the wound so it heals from the inside out. For straightforward abscesses, this alone is often enough.
Problems arise when bacteria escape that walled-off pocket and spread into surrounding tissue, causing cellulitis, a rapidly expanding area of red, warm, swollen skin. If the infection enters the bloodstream, it can lead to sepsis, a life-threatening condition. Warning signs that an abscess has progressed include a fever, a red rash that’s spreading or changing quickly, and feeling systemically unwell. A rapidly growing area of redness around an abscess, even without a fever, warrants medical attention within 24 hours.
Why Some Abscesses Keep Coming Back
Recurrent abscesses are frustrating, and they usually point to an ongoing source of bacteria or an underlying condition. Persistent staph colonization on the skin or in the nose is the most common reason. In households where one person carries MRSA, the bacteria can cycle between family members through shared towels, razors, or surfaces.
Recurring abscesses in skin folds, especially if they leave scars or tunneling wounds, may signal hidradenitis suppurativa rather than simple staph infections. The distinction matters because hidradenitis suppurativa requires a different treatment approach focused on reducing inflammation and preventing flares, not just draining individual abscesses. If you notice abscesses returning to the same areas, particularly the groin, armpits, or under the breasts, that pattern is worth bringing to a dermatologist’s attention.