How Do You Get a Staph Infection? Causes and Risks

Staph infections begin when Staphylococcus aureus, a bacterium that already lives harmlessly on the skin or inside the nose of roughly a third of the population, finds a way past the body’s defenses. A cut, a scrape, a surgical incision, a weakened immune system, or even chronically dry and cracked skin can give the bacteria an entry point. The real surprise for most people is that the source of the infection is often their own body, not some exotic germ picked up from a stranger.

Most People Already Carry the Bacteria

About 30% of people carry S. aureus in their nose at any given time without any symptoms at all.¹ Some are persistent carriers who harbor it year-round; others are intermittent carriers who pick it up and lose it periodically.² The nostrils are the primary reservoir, but the bacteria also colonize the throat, armpits, and groin. This colonization is not itself an infection. The bacterium behaves as a quiet resident, kept in check by the surrounding microbial community and by intact skin. The problem starts when it migrates from those colonization sites to a vulnerable spot, like a wound or a catheter insertion point.

Carrying staph in your nose does raise your odds of developing an actual infection. Your own hands transfer the bacteria from your nostrils to other parts of your body dozens of times a day without you noticing. That is why nasal carriers are disproportionately represented among people who develop post-surgical staph infections, and why hospitals sometimes screen patients’ noses before major operations.

What Lets the Bacteria Through

Healthy, unbroken skin is a remarkably effective barrier. The skin’s resident microbes compete with S. aureus for space and resources, and the physical barrier of intact skin keeps the bacterium on the outside where it can do no harm. An infection develops when something disrupts that barrier.

The most obvious disruption is a wound. Cuts, scrapes, insect bites, surgical incisions, injection sites, and burns all create openings. But less dramatic damage works too. Razor burn, chafing from clothing or sports equipment, and cracked skin from dryness or frequent handwashing can provide enough of a breach for staphylococci to slip beneath the surface.

Chronic skin conditions multiply the risk considerably. People with eczema (atopic dermatitis) carry S. aureus on their skin at far higher rates than the general population, and the colonization tracks with disease severity.³ One study found that nearly 58% of eczema patients had nasal colonization and a similar proportion had colonization on their eczema lesions, compared with about 30% colonization on their unaffected skin.⁴ The inflamed, cracked skin of an eczema flare is essentially a welcome mat for the bacterium.

Diabetes and Immune Compromise

Diabetes is one of the strongest systemic risk factors for staph infection. People with poorly controlled blood sugar face more frequent and more invasive S. aureus infections than the general population.⁵ The reasons are layered. High glucose levels in the blood and tissues essentially provide extra fuel for the bacteria. At the same time, diabetes impairs the immune cells that would normally rush to the site of an infection and kill the invaders.⁶ Diabetic neuropathy reduces sensation in the feet and lower legs, meaning small cuts and blisters go unnoticed and untreated for longer, giving bacteria a wider window to establish an infection.

Other conditions that suppress the immune system raise similar risks. People undergoing chemotherapy, organ transplant recipients taking anti-rejection drugs, and those with HIV/AIDS all face higher rates of staph infection. So do people on long-term corticosteroid therapy and those with chronic kidney disease requiring dialysis, who have repeated needle punctures and catheter access that create consistent entry points.

Where You Pick It Up Outside Your Own Body

While self-infection from your own nasal carriage is the most common pathway, staph also spreads from person to person and from contaminated surfaces. Direct skin-to-skin contact is the most efficient route. Shared towels, razors, and athletic equipment also transmit the bacteria. S. aureus can survive on inanimate surfaces for hours to months depending on the material and conditions.⁷

Gyms are a well-documented transmission site. Studies culturing gym equipment have repeatedly found S. aureus on weight benches, handles, and mats.⁸ One study concluded that gymnasium equipment is a meaningful reservoir for the bacteria and could play a real role in spreading it to users.⁹ The combination of sweaty skin, minor abrasions, and shared surfaces makes the gym a particularly favorable environment for transmission.

Contact sports amplify the risk further. A prospective study of collegiate athletes found that those in contact sports had more than twice the odds of carrying MRSA compared with non-contact sport athletes, and they tended to carry the bacteria for longer periods.¹⁰ Wrestling, rugby, and football create the perfect storm: frequent skin-to-skin contact, abrasions, shared locker room facilities, and equipment that traps moisture.

Healthcare Settings and Medical Devices

Hospitals and other healthcare facilities remain significant sources of staph infection. Any device that penetrates the skin, whether a central venous catheter, a urinary catheter, or a prosthetic joint, creates a direct route past the body’s barrier defenses. In studies of catheter-related bloodstream infections, S. aureus is consistently one of the most common causes, and heavy colonization at the insertion site dramatically increases the odds of infection.¹¹

One reason medical devices are so vulnerable is that S. aureus excels at forming biofilms, sticky microbial communities that coat the surface of implanted materials. Once a biofilm is established, antibiotics have a much harder time penetrating it, and the immune system’s white blood cells struggle to clear the infection.¹² Biofilm-related infections on prosthetic joints or heart valves often require removing the device entirely because antibiotics alone cannot wipe out the protected colony.¹³

Community Staph vs Hospital Staph

Not all methicillin-resistant S. aureus (MRSA) is the same. For decades, MRSA was almost exclusively a hospital problem. Then, starting in the late 1990s, infections began appearing in otherwise healthy people with no connection to healthcare settings. These community-acquired (CA-MRSA) strains turned out to be genetically distinct from their hospital-acquired (HA-MRSA) cousins.¹⁴

The practical differences matter. CA-MRSA tends to cause skin and soft-tissue infections: boils, abscesses, and cellulitis. HA-MRSA more often causes pneumonia, bloodstream infections, and surgical site infections. In a study comparing the two in Sacramento, California, nearly 45% of all MRSA infections were community-acquired, and the dominant community strain (USA300) was genetically unrelated to the dominant hospital strain (USA100).¹⁵ That same study found injecting drug users accounted for about half of CA-MRSA infections, underscoring needle sharing as a major risk factor.

CA-MRSA strains also tend to be more susceptible to antibiotics beyond the standard beta-lactams. A large analysis from a Chinese hospital found CA-MRSA was highly sensitive to drugs like vancomycin, linezolid, ciprofloxacin, and gentamicin, while HA-MRSA isolates showed much broader resistance.¹⁵ That difference is partly because community strains carry smaller resistance elements and have not been shaped by the intense antibiotic pressure of a hospital environment.

Pets and Livestock as Sources

Staph does not respect the species barrier. Household pets, particularly dogs and cats, can carry MRSA strains and transmit them to their owners. The MRSA clones identified in pets frequently match the clones circulating among humans in the same geographic area, suggesting that pets and owners pass the bacteria back and forth.¹⁶ If someone in a household has a recurring staph infection, the family pet is worth considering as a possible re-infection source.

Livestock represent a separate pathway. A lineage known as MRSA CC398 originated in farm animals and can spread to people through direct contact with animals, exposure to contaminated farm environments, and handling or eating undercooked contaminated meat.¹⁷ Farmers, slaughterhouse workers, and veterinarians face the highest risk from this route. Livestock-associated strains do not typically spread as easily between people as the classic community strains do, but they can cause serious infections in the individuals who acquire them.

When Staph Goes Deeper

Most staph infections stay in the skin and resolve with proper treatment. The danger comes when the bacteria enter the bloodstream, a condition called bacteremia. From the blood, S. aureus can seed distant organs, leading to endocarditis (infection of the heart valves), osteomyelitis (bone infection), septic arthritis, or abscesses in the lungs, kidneys, or brain. S. aureus is one of the leading causes of life-threatening bloodstream infections worldwide.

Certain staph strains also produce toxins that cause illness even without deep tissue invasion. Toxic shock syndrome is perhaps the best-known toxin-mediated staph disease. It can develop from tampon use during menstruation or from wound infections after surgery, and it escalates rapidly to organ failure if not treated promptly. Staphylococcal food poisoning is another toxin-driven illness: the bacteria grow in improperly stored food and release heat-stable toxins that cause vomiting and diarrhea within hours of eating.

Other Staphylococci You Should Know About

S. aureus gets the most attention, but it is only one species in a large genus. The coagulase-negative staphylococci (CoNS), a group that includes species like S. epidermidis, S. haemolyticus, and S. lugdunensis, live on everyone’s skin as normal residents. For a long time, when these species showed up in lab cultures, they were dismissed as contaminants. That view has changed. CoNS are now recognized as major causes of infections associated with implanted medical devices, particularly in intensive care settings and in premature newborns.¹⁸

S. lugdunensis deserves special mention because it behaves more aggressively than most CoNS, sometimes mimicking S. aureus in its ability to cause endocarditis. S. saprophyticus is a common cause of urinary tract infections in young women. And CoNS skin infections, while less common than those caused by S. aureus, tend to show up as abscesses and nail-bed infections, especially in elderly or immunocompromised people.¹⁹

Why Some People Get Infections and Others Do Not

Two people can carry the same staph strain in their noses, get the same small cut, and have completely different outcomes. Part of the explanation is genetic. Genome-wide studies have identified variations in genes involved in the immune response, including ones related to certain immune signaling molecules and antimicrobial peptides, that influence whether someone becomes a persistent carrier and how likely they are to develop an invasive infection if the bacteria enter the blood.²⁰ One study looking specifically at endocarditis (heart valve infection) during staph bacteremia found genetic variants on chromosome 3 that appeared to protect some people from that particular complication.²¹

This research is still in its early stages. Nobody is getting a genetic test to predict their staph infection risk yet. But it helps explain a frustrating clinical reality: some patients suffer recurrent staph infections despite doing everything right, while others seem oddly resistant. The interplay between bacterial virulence factors and host genetics is a two-sided equation, and we are only beginning to read the host side.

Reducing Your Risk

The single most effective everyday prevention measure is boring but true: wash your hands thoroughly with soap and water. Alcohol-based hand sanitizers also work well against S. aureus. Beyond hand hygiene, keeping cuts and scrapes clean and covered until they heal is critical. If you use shared gym equipment, wiping it down before and after use with a disinfectant is a simple step that reduces surface contamination.

For people heading into surgery, hospitals increasingly use a decolonization protocol. Applying mupirocin ointment inside the nostrils before the operation kills the bacteria in the primary reservoir. A meta-analysis of randomized trials found that mupirocin-based decolonization cut the rate of staph surgical site infections by about a third, and the effect was even stronger when combined with chlorhexidine body washes and when targeted specifically at confirmed carriers.²² Another analysis found that the combination of mupirocin and chlorhexidine reduced surgical site infection risk by about 60%.²³

For people who suffer recurrent staph skin infections outside the hospital, doctors sometimes prescribe a similar decolonization regimen: mupirocin in the nose plus chlorhexidine washes for several days. Household contacts may be treated simultaneously to prevent the ping-pong effect of family members recolonizing each other.

The Resistance Problem and Why It Keeps Getting Worse

MRSA emerged because S. aureus acquired a mobile genetic element called SCCmec, which carries the gene for methicillin resistance. This element has been picked up independently by different staph lineages many times over the decades, and major MRSA clones have arisen repeatedly from successful epidemic strains that were already good at spreading. Isolates with decreased susceptibility to vancomycin, long considered the antibiotic of last resort, have emerged from some of these same successful lineages.²⁴ The depressing pattern is one of incremental escalation: the bacteria that are best at colonizing and spreading are also the ones most likely to acquire new resistance tools.

Rapid diagnostic tests are one countermeasure gaining ground. Traditional blood cultures take one to two days to identify the species and its resistance profile, which means doctors often start with broad-spectrum antibiotics and adjust later. Newer molecular tests can detect MRSA directly from blood samples in hours rather than days, allowing clinicians to narrow therapy faster and reduce unnecessary antibiotic use.²⁵ Faster identification means the right drug sooner and less selective pressure for resistance across the hospital.