Allergic diseases are among the leading causes of chronic morbidity worldwide, affecting over a third of the population and encompassing conditions such as allergic rhinitis, bronchial asthma, atopic dermatitis, urticaria, and allergic conjunctivitis, largely mediated by type I hypersensitivity (1). Their rising prevalence imposes substantial burdens on quality of life, productivity, healthcare costs, and (for athletes) training and performance (2).

In sport, allergic disease deserves particular attention in disciplines with high cardiorespiratory demand and indoor practice, where suboptimal ventilation and exposure to chemical agents can exacerbate respiratory symptoms (3). Multiple studies consistently report higher rates of respiratory complaints and diagnosed allergic disease in swimmers compared with athletes from land-based sports (4, 5). Further evidence suggests that swimmers may present more symptoms and a higher use of medication than endurance athletes in disciplines such as athletics or cycling (5).

Swimming entails repetitive contact with chlorinated water and (in indoor venues) volatile disinfection byproducts, notably chloramines, which act as airway irritants and can increase epithelial permeability and airway inflammation. Competitive swimmers, including elite cohorts, consistently show elevated respiratory morbidity, with asthma prevalences among the highest across sports (often >40%) and increased allergic and rhinitis symptoms (4, 6–12). Mechanistic and epidemiological studies link these findings to prolonged exposure to water disinfection by-products, such as chloramines and trichloroisocyanuric acid, particularly in heated indoor pools (13–15). Other studies show signs of airway inflammation even in the absence of a formal asthma diagnosis, underscoring the physiopathological impact of aquatic exposure on respiratory function in this athletic population (8–12).

Experimental and field studies have clarified the biological pathway through which these exposures exert their effects. Volatile chloramines, especially trichloramine, can disrupt epithelial tight-junctions, increase airway epithelial permeability, induce oxidative and nitrosamine stress, and activate inflammatory cascades that facilitate immune sensitization to inhaled allergens (16–18). When volatilization is enhanced by higher water temperatures and ventilation is suboptimal, airborne concentrations may rise substantially, increasing inhalational dose during exercise (19). Repeated exposure under high ventilatory demand may contribute not only to acute irritation but also to chronic epithelial remodeling, which has been documented among competitive swimmers (20, 21). These mechanisms help contextualize the elevated burden of allergy-compatible symptoms observed in aquatic athletes.

Despite this, most evidence is derived from elite or Olympic cohorts and/or resource-intensive physiological testing that is less feasible for population-level surveillance (3, 4, 22). Few studies have incorporated standardized, sport-adapted screening tools suitable for broad application (23, 24). Comparative research with other sports further supports a specific association between swimming, bronchial hyperreactivity, and allergic symptoms—often more pronounced in younger athletes. It must also be acknowledged that common symptoms such as cough, sneezing, ocular pruritus, or wheeze can arise from non-allergic conditions, including recurrent viral infections, active or passive smoking, or environmental pollution; household ventilation and the use of cleaning chemicals may constitute relevant, unmeasured confounders in several studies (25). These gaps underscore the need for pragmatic, validated screening approaches in real-world settings.

Given these gaps, practical tools such as standardized clinical questionnaires are particularly valuable for large-scale, sport-relevant screening. The Allergy Questionnaire for Athletes (AQUA) is a 21-item tool assessing respiratory, ocular, and cutaneous symptoms; scores ≥5 indicate allergy-compatible manifestations. While validated across languages and contexts, evidence has mainly focused on elite swimmers. This study uses AQUA to characterize the prevalence and correlations of allergy-compatible symptoms in non-elite, federated swimmers, addressing this gap. Therefore, the current study aimed to estimate the prevalence of AQUA-positive screening among competitive swimmers aged ≥16 years and to examine associations between symptoms and demographic, training, and pool-environment variables in Portugal. Secondary aims were to describe self-reported diagnoses, medication use, and to explore independent predictors of AQUA positivity.

Based on existing evidence, we hypothesized that, although federated swimmers experience lower cumulative exposure than elite swimmers, their regular training in chlorinated pools would still result in a prevalence of allergy-compatible symptoms higher than that observed in the general population. Furthermore, we hypothesized that environmental conditions (such as water temperature and perceived air quality) and individual characteristics (including age, sex, and weekly training frequency) would be significantly associated with AQUA positivity. Understanding these relationships may support more informed decisions by coaches, clinicians, and pool operators regarding early symptom recognition, appropriate referral, and environmental management strategies.

This study aimed to characterize the prevalence and correlations of allergy-related symptoms in a national cohort of non-elite competitive swimmers using the validated AQUA questionnaire. We found that four in five swimmers screened AQUA-positive, a prevalence markedly higher than general-population estimates and consistent with international evidence documenting increased respiratory morbidity among swimmers. These findings demonstrate that the burden of allergic and respiratory symptoms extends beyond Olympic and elite cohorts, underscoring the relevance of systematic surveillance in federated contexts.

Competitive swimmers—including elite cohorts—have consistently shown elevated respiratory morbidity, with asthma prevalences among the highest across sports (often >40%) and increased allergic and rhinitis symptoms (4, 6–12). The symptom pattern in our cohort—dominant upper-airway involvement with frequent cough and ocular symptoms—is consistent with irritant effects from chlorinated water and volatile by-products, especially in heated, indoor pools (13–15). Airway inflammation has been observed even without a formal asthma diagnosis, underscoring the physiopathological impact of aquatic exposure on respiratory function in this athletic population (8–12).

Volatile chloramines, particularly trichloramine, have been shown to disrupt epithelial tight junctions, increase airway permeability, and activate inflammatory pathways that promote immune sensitization and chronic airway remodeling (16, 20, 26). These mechanisms are biologically plausible and help explain the elevated burden of symptoms observed in swimmers.

Chronic airway irritation may also impair respiratory efficiency and oxygen uptake during exercise. Studies using exhaled breath analysis and metabolomic profiling have demonstrated altered respiratory parameters in swimmers exposed to chlorinated environments, suggesting that repeated exposure may compromise ventilatory performance and aerobic capacity (17, 27).

Significant associations were observed with sex, age, training frequency, and water temperature. Female swimmers presented a higher prevalence of AQUA positivity, in agreement with studies suggesting sex-based susceptibility to allergic disease (28, 29). Younger age (16–25 years) was also a risk factor, consistent with data showing that allergy incidence peaks in adolescence and early adulthood (1, 30). Training frequency emerged as an independent predictor, supporting the role of cumulative exposure to chlorinated water and air by-products in symptom development (31, 32). The temperature gradient (≥25 °C vs. ≤25 °C) is biologically plausible given the favored formation/release of chlorination by-products at warmer temperatures (16, 26). Several variables—including perceived air quality, pool setting, and years of federated practice—were not significantly associated with AQUA-positive screening. These non-significant findings suggest that, within this non-elite swimming population, symptom burden may be more strongly driven by individual susceptibility and training volume than by broad contextual or exposure-duration factors. Nevertheless, the absence of significance does not exclude potential subtle effects that might become apparent with objective environmental monitoring or larger samples.

Contrary to expectations, no significant associations were found for years federated, self-reported training intensity, pool setting (indoor vs. outdoor), or use of respiratory protective equipment. Several explanations are plausible. First, exposure misclassification is likely: years federated, and a single self-rated intensity item are imprecise surrogates of cumulative dose (they do not capture session duration, rest intervals, or ventilation patterns), which can attenuate true effects toward the null. Second, limited between-group contrast may have reduced power—most swimmers trained predominantly indoors (≈80%), leaving little variability to detect setting-related differences, while protective equipment was infrequently and heterogeneously used (e.g., nose clips vs. masks), and adherence was not measured. Third, collinearity with stronger acute exposures may have masked associations: training frequency and water temperature, both more proximate determinants of chloramine exposures, showed clear effects, whereas years federated and intensity may partly operate through these variables. Fourth, sample size constraints (n = 95) limit precision for modest effects and subgroup analyses, yielding wide confidence intervals. Finally, confounding by indication and reverse causality are possible: swimmers with more symptoms might preferentially use protective gear or avoid certain settings, biasing observed associations toward no effect. The non-significant trend for perceived air quality likely reflects subjective variability and the low sensitivity of self-report to ventilation performance (e.g., air-change rates, combined chlorine levels), which were not instrumentally measured.

It is important to clarify that AQUA is a screening tool rather than a diagnostic test, designed to identify athletes with symptoms compatible with allergic disease. A positive screen does not equate to a clinical diagnosis, and confirmation through objective testing (e.g., spirometry, IgE assays, skin prick tests) remains essential (23).

The strong associations with prior diagnosis and medication reinforce internal consistency between screening signals and care pathways, while the subset of AQUA-positive swimmers without a formal diagnosis suggests potential under-recognition. Incorporating standardized questionnaires such as AQUA into routine club-level screening could facilitate early referral to medical evaluation and optimize symptom control.

This study demonstrated a high prevalence of allergy-related symptoms among federated swimmers, with more than four out of five athletes screening positive on the AQUA questionnaire. Symptom burden was strongly associated with female sex, younger age, higher training frequency, and warmer water temperatures. These findings highlight the importance of systematic screening in federated swimming contexts and support the use of validated tools such as AQUA for early identification of athletes at risk.

The results also emphasize the role of pool environmental management, particularly ventilation and water temperature control, in mitigating respiratory and allergic morbidity. Implementation of structured screening protocols in clubs and federations may enable timely medical referral, optimize treatment, and minimize the impact of allergic disease on both performance and overall health. Future studies combining clinical evaluation with environmental monitoring are warranted to consolidate these findings and guide preventive strategies.