How Do You Get Cellulitis: Causes and Risk Factors

Cellulitis develops when bacteria enter through a break in the skin and infect the deeper layers of tissue underneath. The infection spreads through the dermis and the fat beneath it, producing the characteristic redness, warmth, swelling, and tenderness that expand outward from the entry point. The bacteria responsible are usually common residents of the skin or environment, and what determines whether you get cellulitis has less to do with encountering dangerous germs and more to do with whether something has compromised your skin’s ability to keep them out.

Which Bacteria Cause It

In the roughly 15% of cellulitis cases where a specific organism is identified, the culprits are almost always beta-hemolytic streptococcus and Staphylococcus aureus.¹ That number is not a typo: in the vast majority of cases, doctors treat cellulitis empirically because blood cultures and wound cultures usually come back negative. The infection is buried in tissue rather than floating in the bloodstream, making it hard to pin down the exact species. This is one reason cellulitis treatment relies heavily on clinical judgment rather than lab results.

Streptococcus, particularly Group A strep, is the most common cause of non-purulent cellulitis, meaning the type that produces spreading redness without an obvious pocket of pus. Staphylococcus aureus, including the methicillin-resistant strain known as MRSA, tends to cause purulent cellulitis with abscesses. The distinction matters for treatment because the two bacteria respond to different antibiotics, but the risk factors for developing either type overlap considerably.

How Bacteria Get In

Your skin is a barrier, and cellulitis almost always requires a breach in that barrier. The break does not have to be dramatic. A small cut, a scratch, a cracked cuticle, a surgical incision, an insect bite, or even dry fissured skin between the toes can provide the opening bacteria need. A systematic review and meta-analysis of risk factors for leg cellulitis found that having any wound carried roughly a 19-fold increase in risk, while a current leg ulcer raised it about 14-fold.² A case-control study from France similarly found that disruption of the skin barrier, including wounds, leg ulcers, fissured toe-web skin, and pressure ulcers, was associated with a roughly 24-fold increase in risk for erysipelas of the leg, a closely related superficial form of cellulitis.³

What makes this tricky is that the entry point can be surprisingly subtle. Many people who develop cellulitis cannot identify a specific injury. Microscopic cracks in the skin, particularly on the feet or lower legs, are enough. If your skin is chronically dry, eczematous, or irritated, the barrier function is already weakened even without visible wounds. A case-control study in a tertiary center found that eczema and skin conditions causing excoriation were independent risk factors, alongside more obvious culprits like ulceration.⁴

Foot Fungus as a Hidden Gateway

Athlete’s foot does not sound like a serious medical problem, and most people treat it as a minor annoyance. But fungal infections of the feet are one of the most consistent and well-documented risk factors for leg cellulitis. The connection is straightforward: fungal infections cause cracking and maceration of the skin between the toes, and those soggy little fissures become entry points for bacteria.

A case-control study published in Dermatology found that fungal infection of the foot roughly doubled the odds of developing acute bacterial cellulitis of the leg, while athlete’s foot specifically affecting the spaces between the toes tripled the odds.⁵ The meta-analysis of leg cellulitis risk factors confirmed these numbers, finding a roughly threefold increase in risk associated with tinea pedis.² A separate prospective study found a similar association when the analysis accounted for bacterial colonization already present in the toe webs.⁶

This is one of the most actionable risk factors for cellulitis because it is treatable. If you have recurring cellulitis of the leg, checking for and treating fungal infections of the feet, including toenail fungus, is one of the first things clinicians should address. The meta-analysis authors explicitly recommended treating modifiable risk factors including toe-web intertrigo alongside antibiotic treatment for cellulitis itself.²

Swelling, Lymphedema, and Venous Disease

Anything that causes chronic swelling of the legs substantially raises the risk of cellulitis. Lymphedema, the accumulation of fluid due to a damaged or overwhelmed lymphatic system, is one of the strongest individual risk factors. The French case-control study found that lymphedema was associated with more than a 70-fold increase in odds of leg erysipelas.³ The pooled meta-analysis estimate was more conservative but still striking, at roughly sevenfold.² The wide range across studies reflects how differently lymphedema is defined and measured, but the direction is consistent: swollen limbs get infected far more often.

The reasons are both mechanical and immunological. Swollen tissue stretches and thins the skin, creating microbreaks. The accumulated fluid is also protein-rich, providing a friendly growth environment for bacteria. And lymphedema itself represents a failure of the lymphatic system, which is a key part of immune surveillance in the skin. Evidence indicates that lymphedema of any cause makes the affected limb susceptible to cellulitis with both greater frequency and greater severity.⁷

Chronic venous disease, where the veins in the legs fail to return blood efficiently, creates a related but distinct pathway. When venous pressure builds up, fluid leaks into surrounding tissue, the skin develops inflammatory changes like stasis dermatitis, and ulcers can form. Cellulitis is a common complication of severe chronic venous disease, particularly when dermatitis or ulceration is present, though edema and lymphatic dysfunction also play a role beyond the obvious skin breakdown.⁸ The tertiary center case-control study found venous insufficiency to be an independent risk factor with roughly tenfold increased odds.⁴

Obesity as an Independent Risk Factor

Being significantly overweight raises your cellulitis risk through multiple pathways, and the data suggest that excess body fat is a risk factor on its own, not just because it tends to co-occur with diabetes or venous disease. A meta-analysis pooling seven case-control studies found that obesity was associated with roughly 2.7 times the odds of developing cellulitis.⁹ A cohort study that specifically separated people by metabolic health found that higher BMI increased cellulitis risk in both metabolically healthy and metabolically unhealthy individuals, indicating that excessive fat tissue itself is the driver.¹⁰

The mechanisms are plausible. Extra weight increases pressure on the lower limbs, promotes venous insufficiency and edema, impairs lymphatic drainage, and changes the local immune environment. Skin folds create warm, moist areas where bacteria thrive and skin breaks down. Being overweight was also independently associated with the recurrence of lower limb cellulitis in a study that found it carried nearly sixfold increased odds of recurrence on logistic regression.¹¹

Diabetes, Immunosuppression, and Aging Skin

Diabetes is widely recognized as a risk factor for skin and soft tissue infections, though its relationship with cellulitis is more nuanced than many people assume. Diabetes impairs white blood cell function, slows wound healing, and is often accompanied by peripheral neuropathy, meaning you might not notice small injuries on your feet. A Taiwanese cohort study of patients with type 2 diabetes found that metformin use was associated with modestly higher rates of cellulitis compared to non-use, though the study’s authors suggested this may partly reflect the fact that metformin users had more advanced disease requiring treatment.¹² The practical takeaway for people with diabetes is that meticulous foot care and prompt attention to any skin break matters enormously.

Immunosuppression from any cause raises cellulitis risk. This includes medications like long-term corticosteroids, chemotherapy agents, and drugs used to prevent organ transplant rejection. Prolonged corticosteroid use has been linked to atypical presentations of cellulitis, including infections caused by organisms that would rarely trouble a healthy immune system. A case report described cellulitis caused by the fungus Candida albicans in a patient on long-term betamethasone injections, highlighting how immunosuppression can open the door to unusual pathogens.¹³ Immunocompromised patients are at particular risk for fungal cellulitis, which can be misidentified as the bacterial form and lead to delayed appropriate treatment.¹⁴

Older age is another factor, largely because aging skin becomes drier, thinner, and less elastic. Declining natural oil production weakens the skin’s barrier function, making it more vulnerable to infections and inflammatory conditions.¹⁵ Regular moisturizing of the lower legs is a simple intervention that can help maintain skin integrity in older adults.

Animal Bites and Scratches

Dog and cat bites and scratches are a distinct route to cellulitis that involves a different set of bacteria. Pasteurella multocida, a bacterium carried in the mouths of most cats and many dogs, is a common cause of rapidly developing cellulitis at the site of a bite or scratch.¹⁶ Cat bites are particularly high-risk because a cat’s narrow, sharp teeth can puncture deep into tissue and deposit bacteria in a spot that quickly seals over at the surface, creating an ideal environment for infection. One review noted that Pasteurella multocida is the major cause of hand infections following domestic animal bites, yet it is apparently often overlooked as a pathogen.¹⁷

People with liver disease are at particularly elevated risk from animal-associated infections. A report described Pasteurella multocida bloodstream infections in patients with liver cirrhosis following non-bite animal exposure, where even routine contact with a pet was enough to trigger serious infection.¹⁸ If you have chronic liver disease and a pet scratches or bites you, seeking prompt medical attention is warranted even if the wound looks minor.

Why Cellulitis Keeps Coming Back

One of the most frustrating aspects of cellulitis is its tendency to recur, and a previous episode is by far the single strongest predictor of a future one. The meta-analysis of leg cellulitis risk factors found that a history of prior cellulitis was associated with roughly 40-fold increased odds of developing another episode.² The tertiary center study similarly found prior cellulitis to be the most powerful predictor, with more than 25-fold increased odds.⁴

The reason is partly anatomical. Each episode of cellulitis damages the lymphatic vessels in the affected area. Damaged lymphatics drain fluid poorly, leading to local swelling, which in turn makes the skin more vulnerable to the next episode. This creates a vicious cycle: cellulitis damages lymphatics, damaged lymphatics cause edema, edema promotes cellulitis. Without addressing the underlying swelling, the cycle tends to accelerate.

Preventive antibiotics can help break the cycle, at least temporarily. A large randomized trial found that daily low-dose penicillin cut the recurrence rate from about 37% to 22% over the prophylaxis period.¹⁹ A meta-analysis of prophylaxis trials confirmed that antibiotics roughly halved the risk of recurrence overall.²⁰ The catch is that the benefit disappeared once the antibiotics stopped: recurrence rates equalized between the treatment and placebo groups during the follow-up period after prophylaxis ended.¹⁹ This underscores that long-term prevention depends on managing the modifiable risk factors, particularly edema, skin breakdown, and fungal infections, rather than relying on antibiotics indefinitely. A review of prophylaxis strategies noted that antibiotic prophylaxis is effective but its role is limited to non-purulent cellulitis where risk factors are appropriately managed.²¹

Occupational and Lifestyle Patterns

Your daily routine can matter more than you might expect. A study examining determinants of recurrent lower limb cellulitis found that occupation was an independent predictor, with recurrence more common among people in certain work categories, particularly those in sedentary business and professional roles or marginal workers, compared to skilled workers. Sitting for long periods, whether for work or rest, was associated with recurrence, likely because prolonged sitting promotes leg swelling and venous stasis.¹¹ A history of local trauma within the preceding week was also significantly associated with recurrence, reinforcing the importance of skin protection in people who know they are at risk.

The study also identified that patients’ level of knowledge about preventing recurrence was itself a predictor, with those who understood less about their condition having higher recurrence rates. This is worth reflecting on: understanding why you keep getting cellulitis and what specific steps reduce your risk, such as treating fungal infections, managing swelling with compression, keeping skin moisturized, and attending promptly to cuts, may itself be protective.

Conditions Commonly Mistaken for Cellulitis

A significant number of people diagnosed with cellulitis do not actually have it. A systematic review and meta-analysis of cellulitis misdiagnosis found that the most common conditions mistaken for cellulitis were stasis dermatitis, eczematous dermatitis, and edema or lymphedema, which together accounted for over half of all misdiagnoses.²² A separate meta-analysis confirmed that the majority of alternative diagnoses were noninfectious, with stasis dermatitis being the single most common.²³

This matters for two reasons. First, if you are being treated repeatedly with antibiotics for presumed cellulitis but not improving, the diagnosis itself may be wrong. Stasis dermatitis can look very similar, producing red, warm, swollen skin on the lower leg, but it stems from venous insufficiency and is treated with compression and skin care rather than antibiotics. Second, overdiagnosis of cellulitis contributes to unnecessary antibiotic use, which carries its own risks. If your leg redness is not getting better with antibiotics, or keeps “recurring” in the same pattern, asking for a dermatology consultation to rule out a noninfectious mimic is reasonable.

Whether Genetics Play a Role

Most of the recognized risk factors for cellulitis are environmental or medical, but there is early evidence that genetic variation may influence susceptibility. A genome-wide study of patients with non-necrotizing erysipelas and cellulitis identified several genetic variants in the promoter region of a gene called AGTR1, which encodes a receptor involved in blood-pressure regulation and vascular function.²⁴ The connection is biologically plausible because AGTR1 influences blood vessel tone and inflammation, both of which affect how well the skin resists and responds to bacterial invasion. That said, the associations were nominal and the field is in its infancy. Nobody is getting a genetic test for cellulitis susceptibility anytime soon. The finding is more useful as a reminder that some people seem to develop cellulitis more easily than their known risk factors would predict, and there may be inherited reasons for that beyond what we can currently measure.

1
JAMA. Cellulitis: A Review
2
PubMed. Risk factors for nonpurulent leg cellulitis: a systematic review and meta-analysis
3
BMJ. Risk factors for erysipelas of the leg (cellulitis): case-control study
4
PubMed Central. The risk factors of lower limb cellulitis: A case-control study in a tertiary centre
5
Dermatology. Chronic Dermatomycoses of the Foot as Risk Factors for Acute Bacterial Cellulitis of the Leg: A Case-Control Study
6
Clinical Infectious Diseases. Risk Factors for Acute Cellulitis of the Lower Limb: A Prospective Case-Control Study
7
PubMed Central. Challenges of cellulitis in a lymphedematous extremity: a case report
8
PubMed. Spontaneous onset of bacterial cellulitis in lower limbs with chronic obstructive venous disease
9
PubMed Central. Association of Cellulitis With Obesity: Systematic Review and Meta-Analysis
10
PubMed Central. Metabolic Obesity Phenotypes and Risk of Cellulitis: A Cohort Study
11
International Journal of Scientific Research and Technology (IJSRT). Determinants In Recurrence Of Lower Limb Cellulitis
12
PubMed Central. Metformin and the risks of cellulitis, foot infections, and amputation in patients with type 2 diabetes
13
PubMed Central. A Case Report of Candidiasis Cellulitis in Long-Term Corticosteroid Use
14
PubMed Central. Diagnostic and therapeutic challenges of treating opportunistic fungal cellulitis: a case series
15
PubMed. What you need to know about common skin problems in older adults
16
JAMA. Pasteurella multocida: Infections After Domestic Animal Bites and Scratches
17
PubMed. Pasteurella multocida–the major cause of hand infections following domestic animal bites
18
PubMed. Pasteurella multocida bacteremia due to non-bite animal exposure in cirrhotic patients: report of two cases
19
PubMed. Penicillin to prevent recurrent leg cellulitis
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PubMed. Antibiotic prophylaxis for preventing recurrent cellulitis: a systematic review and meta-analysis
21
PubMed Central. Recurrent Cellulitis: Who is at Risk and How Effective is Antibiotic Prophylaxis?
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PubMed Central. Misdiagnosis of Uncomplicated Cellulitis: a Systematic Review and Meta-analysis
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PubMed. Prevalence of misdiagnosis of cellulitis: A systematic review and meta-analysis
24
PubMed Central. Genetic Susceptibility to Non-Necrotizing Erysipelas/Cellulitis