Cellulitis is a bacterial infection of the skin and the soft tissue beneath it, most often caused by streptococci or staphylococci that slip through cracks in the skin’s protective barrier. The result is a red, hot, swollen and painful area of skin, usually on the lower legs, often accompanied by fever and malaise. Although antibiotics can usually clear the infection, cellulitis imposes a substantial burden on health systems, because severe cases require intravenous therapy and hospital admission, and a considerable share of patients return with new episodes months or years later. Despite how frequently clinicians encounter the disease, risk factors reported in the literature have been inconsistent, which is precisely the gap the Vienna team set out to close.

The researchers designed their investigation as a retrospective case-control study, a design that compares people who have a condition with people who do not, and then looks backward to identify exposures or characteristics that differ between the two groups. In this case, the cases were 1,395 patients treated for cellulitis, while the controls numbered 667. Using regression models, the team analyzed which variables were associated with three distinct outcomes: the initial development of cellulitis, the occurrence of recurrent episodes, and prolonged hospitalization. Statistical models of this kind produce odds ratios, figures that express how much more likely an outcome is in the presence of a given factor, together with confidence intervals that indicate the precision of the estimate and p-values that signal statistical significance.

The results paint a remarkably consistent picture. Male sex emerged as a strong risk factor for developing cellulitis in the first place, with an odds ratio of 2.68, meaning men in the dataset had nearly triple the odds of women. Higher baseline age also mattered, with each additional year of age modestly but significantly raising the odds, reflected in an odds ratio of 1.03 per year. These demographic findings align with the clinical intuition that older patients and male patients are overrepresented on wards treating soft tissue infections, but the study places those impressions on firm quantitative footing.

The most striking findings concerned breaches of the skin barrier, which dwarfed every other risk factor in magnitude. Patients with tinea pedis, the fungal infection commonly known as athlete’s foot, had an odds ratio of 72.48 for developing cellulitis, an enormous effect that underscores how the fissures and scaling produced by a seemingly minor fungal problem can open the door to serious bacterial invasion. Ulcers carried an odds ratio of 45.79, traumatic wounds an odds ratio of 229.26, stasis dermatitis an odds ratio of 10.81, and eczema an odds ratio of 13.14. In other words, almost any condition that compromises the integrity of the skin, whether through inflammation, ulceration or injury, dramatically multiplies the risk that bacteria will gain entry and establish an infection in the underlying tissue.

Fluid-related conditions formed a second major cluster of risk. Venous insufficiency, in which faulty valves in the leg veins allow blood to pool and fluid to leak into the tissues, was associated with an odds ratio of 2.36. Lymphoedema, the swelling that results from impaired drainage of lymph fluid, carried an odds ratio of 11.21, and oedema not otherwise specified an odds ratio of 13.12. The biological logic is compelling: fluid-rich, swollen tissue is thought to impair local immune defenses and circulation, creating an environment in which bacteria that have breached the skin can proliferate more easily. Clinicians have long observed that patients with chronically swollen legs are prone to cellulitis, and this study quantifies just how pronounced that vulnerability is.

Metabolic and chronic systemic conditions also left their mark. Diabetes mellitus was associated with an odds ratio of 1.58 for disease onset, chronic kidney disease with an odds ratio of 2.29, and obesity with an odds ratio of 2.74. Each of these conditions is known to affect immunity, tissue perfusion or wound healing in ways that could plausibly facilitate infection. Diabetes impairs both immune cell function and microvascular circulation, chronic kidney disease is linked to immune dysfunction and fluid overload, and obesity is associated with chronic low-grade inflammation, altered lymphatic drainage and skin fold problems that can compromise the barrier function of the skin.

Perhaps the most clinically consequential finding is that obesity did not merely raise the risk of a first episode. It was also a consistent risk factor for multiple disease episodes, with an odds ratio of 1.73, and for prolonged hospitalization, with an odds ratio of 1.72. This means that patients with obesity were not only more likely to develop cellulitis in the first place but also more likely to experience the disease repeatedly and to require longer hospital stays when they did. In an era when obesity rates continue to climb globally, this finding suggests that the burden of cellulitis on health systems may grow in parallel, and it highlights weight management as a potential long-term strategy for reducing both the incidence and the severity of the disease.

The authors conclude that male sex, higher age, breaches of the skin barrier, oedema, diabetes mellitus, chronic kidney disease and obesity may act as strong risk factors for cellulitis, with obesity additionally predisposing patients to recurrent episodes and extended hospitalization. The practical implications are significant. For patients with athlete’s foot, ulcers, eczema or leg swelling, meticulous skin care and prompt treatment of these conditions could represent a highly effective form of prevention, given the enormous odds ratios attached to barrier defects. For patients with lymphoedema or venous insufficiency, compression therapy and careful management of swelling may reduce infection risk. And for the growing population of patients with obesity, the study adds another compelling reason to address weight as a modifiable factor in infectious disease risk.

As with any retrospective case-control study, the findings describe associations rather than proven causal relationships, and the retrospective design means the researchers relied on previously recorded data rather than prospective observation. Nevertheless, the large number of patients analyzed and the breadth of risk factors examined make this one of the most comprehensive assessments of cellulitis epidemiology available. By systematically separating the factors that drive the first infection from those that drive recurrence and prolonged hospital stay, the Vienna team has given clinicians a clearer map of where to focus preventive efforts, from treating fungal foot infections and managing leg swelling to recognizing obesity as a factor that shapes the entire trajectory of this common and costly infection.

Subject of Research: Risk factors for the onset, recurrence and prolonged hospitalization of cellulitis patients

Article Title: Risk factors for onset, recurrence and prolonged hospitalization in patients with cellulitis: a retrospective case-control study

Article References: Borst, C., Steiner, I., Stegmüller, S., Peichl, D., Egger, E., Symmank, D., Chromy, D., & Weninger, W. (2026). Risk factors for onset, recurrence and prolonged hospitalization in patients with cellulitis: a retrospective case-control study. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14500-2

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14500-2

Keywords: cellulitis, skin infection, risk factors, obesity, tinea pedis, lymphoedema, diabetes mellitus, chronic kidney disease, case-control study, hospitalization, dermatology, infectious diseases