Allergic rhinitis (AR) represents a global health challenge, affecting up to 30% of the general population and imposing a substantial burden on quality of life, work productivity, and healthcare expenditure [1,2]. The condition is characterised by immunoglobulin E (IgE)-mediated inflammation of the nasal mucosa following exposure to inhaled allergens, manifesting as sneezing, rhinorrhoea, nasal obstruction, and nasal itching. The Allergic Rhinitis and its Impact on Asthma (ARIA) initiative has provided a comprehensive framework for classification based on symptom duration (intermittent versus persistent) and severity (mild versus moderate-severe), enabling standardised assessment and management [3]. The epidemiology of AR exhibits marked geographic and temporal heterogeneity, largely attributable to variations in local aerobiology. In temperate zones, well-defined pollen seasons lead to predictable peaks in seasonal AR, whereas in tropical and subtropical regions, perennial warm temperatures and high humidity support year-round fungal growth and multiple overlapping pollination periods, blurring the distinction between seasonal and perennial forms [4,5].

India, with its vast climatic diversity, harbours a wide array of aeroallergens that vary considerably between regions and seasons. Studies from northern India have documented a bimodal pollen calendar with tree pollen peaks in spring and weed pollen peaks in autumn [6,7]. Conversely, southern India, particularly Tamil Nadu, experiences two major monsoons the southwest monsoon (June–September) and the northeast monsoon (October–December) each creating distinctive ecological conditions that influence the abundance and type of airborne allergens. The southwest monsoon brings heavy rain and high wind speeds that may disperse grass and weed pollens, while the northeast monsoon, characterised by retreating moisture and dampness, favours the proliferation of moulds and house dust mites [8,9]. Despite these unique climatic patterns, there is a notable paucity of data describing how AR presentations shift across these monsoonal phases in Tamil Nadu, especially in less-studied semi-urban districts such as Perambalur.

Perambalur lies in the central part of Tamil Nadu and is predominantly an agrarian district where cultivation of crops like cotton, maize, and paddy, as well as abundant weed flora, contributes to a complex aerobiological milieu. The Dhanalakshmi Srinivasan Institute of Medical Sciences and Hospital serves as the only tertiary care centre in the region, catering to a large rural and semi-urban population. A preliminary audit of outpatient records suggested that patients with AR reported differing dominant symptoms depending on the time of year, prompting a formal investigation. Understanding local seasonal trends is essential not only for accurate etiological diagnosis but also for planning anticipatory pharmacotherapy and targeted allergen avoidance measures. Moreover, such data can inform regional aerobiological surveillance programmes and public health messaging.

The present study was designed to prospectively characterise the seasonal variation in the clinical presentation of AR among patients attending the ENT outpatient department of our hospital. By comparing two distinct monsoonal periods covering the second half of the calendar year, we aimed to delineate differences in symptom profiles, ARIA classifications, and allergen sensitisation patterns. We hypothesised that the southwest monsoon period would be associated with predominantly pollen-driven symptoms such as sneezing and itching, whereas the northeast monsoon period would be associated with mould-driven symptoms characterised by nasal congestion and rhinorrhoea. The findings are intended to provide a clinical reference that aids otorhinolaryngologists and allergists practising in similar tropical settings.

OBJECTIVE

This study primarily aimed to evaluate and compare the clinical presentation, symptom severity, and allergen sensitisation profiles of AR patients presenting during two distinct monsoonal seasons July to September (southwest monsoon) and October to December (northeast monsoon) at a tertiary care hospital in Perambalur, Tamil Nadu. By quantifying individual nasal symptom scores and classifying patients according to the ARIA guidelines, we sought to delineate season-specific phenotypes. The secondary objective was to identify the most prevalent aeroallergens in each period through skin prick testing, thereby generating a preliminary seasonal allergen calendar relevant to this agro-climatic zone.

Establishing such a seasonal profile is expected to enhance the precision of clinical diagnosis and facilitate season-appropriate management strategies, including the targeted use of antihistamines, intranasal corticosteroids, and allergen-specific immunotherapy. Furthermore, the study aimed to highlight the importance of integrating local aerobiological data into routine ENT practice in under-researched regions of southern India, where seasonal shifts may be under-recognised and patients often receive uniform treatment irrespective of the time of year.

This prospective, cross-sectional observational study was conducted in the Department of Otorhinolaryngology at Dhanalakshmi Srinivasan Institute of Medical Sciences and Hospital, Perambalur, Tamil Nadu, India, over a six-month period from 1st July 2025 to 25th December 2025. The study protocol was approved by the Institutional Ethics Committee, and written informed consent was obtained from all participants. The research period was deliberately chosen to encompass the two dominant monsoonal phases affecting Tamil Nadu: the active southwest monsoon (July–September) and the active-to-waning northeast monsoon (October–December). Perambalur experiences a tropical savannah climate with a mean annual rainfall of approximately 850 mm, predominantly during these two periods. The hospital is a 750-bed tertiary care teaching facility that serves the predominantly agrarian population of Perambalur and surrounding districts, providing a representative sample of the region’s allergic disease patterns. Inclusion criteria: Adults aged 18–65 years with a clinical diagnosis of AR according to the ARIA 2016 guidelines [3], presenting to the ENT outpatient department, and willing to provide written informed consent were included. Patients needed to have been symptomatic for at least one month prior to presentation. Exclusion criteria Patients with acute upper respiratory tract infection, nasal polyposis, severe deviated nasal septum, prior nasal or sinus surgery within the preceding six months, current immunotherapy, use of systemic corticosteroids or antihistamines within one week of assessment, pregnancy, lactation, or any systemic illness that could confound symptom interpretation (e.g., granulomatosis with polyangiitis) were excluded. Patients who had relocated from a different climatic zone within the preceding three months were also excluded to minimise exposure misclassification. Data Collection Procedure Consecutive eligible patients were enrolled after obtaining informed consent. A detailed demographic and clinical history was recorded, including age, sex, occupation, residential address, duration of symptoms, and known triggers. All participants underwent anterior rhinoscopy and nasal endoscopy to rule out structural abnormalities. The Total Nasal Symptom Score (TNSS) was assessed for four cardinal symptoms sneezing, rhinorrhoea, nasal obstruction, and nasal itching each graded on a 0–3 scale (0 = absent, 3 = severe), yielding a maximum total of 12. ARIA classification was assigned based on symptom duration (<4 days per week or <4 consecutive weeks classified as intermittent; otherwise persistent) and impact on daily activities (mild if no troublesome sleep disturbance or impairment of daily activities; moderate-severe if present). Skin prick testing (SPT) was performed on the volar forearm using standardised allergen extracts (Allergo India, New Delhi) against a panel of 15 common aeroallergens: Dermatophagoides pteronyssinus, D. farinae, Parthenium hysterophorus, Prosopis juliflora, Cynodon dactylon, Aspergillus fumigatus, Alternaria alternata, Cladosporium herbarum, Penicillium chrysogenum, Curvularia lunata, cockroach, cat dander, dog dander, and two regional weed pollens (Amaranthus spinosus, Chenopodium album). Histamine dihydrochloride (10 mg/mL) and normal saline served as positive and negative controls, respectively. A wheal diameter ≥3 mm larger than the negative control at 15 minutes was considered positive. All procedures were performed by a single trained investigator to minimise inter-observer variability. Statistical Data Analysis Sample size was calculated based on an anticipated moderate effect size (Cohen’s d = 0.5) for the difference in individual symptom scores between the two seasonal groups, with α = 0.05 and power (1-β) = 0.80, yielding a minimum of 24 participants per group. Thus, a total of 48 patients were enrolled, 24 in each period. Data were entered into Microsoft Excel and analysed using IBM SPSS Statistics version 25.0 (IBM Corp., Armonk, NY, USA). Categorical variables (sex, occupation, ARIA classification, individual allergen sensitisation) were expressed as frequencies and percentages, and inter-season comparisons were made using the chi-square test or Fisher’s exact test as appropriate. Continuous variables (age, duration of symptoms, TNSS and its component scores) were expressed as mean ± standard deviation (SD). Normality was assessed using the Shapiro-Wilk test. Comparisons between Group A (July–September) and Group B (October–December) were performed using the independent samples t-test for normally distributed data and the Mann-Whitney U test for skewed data. A two-sided p-value <0.05 was considered statistically significant.

A total of 48 patients fulfilling the inclusion criteria were enrolled, with equal distribution across the two monsoonal periods (Group A: n=24, July–September; Group B: n=24, October–December). The demographic characteristics of the study population are summarised in Table 1. The overall mean age was 34.2±11.4 years, and there was no significant difference in age distribution between the groups (p=0.61). Females constituted 54.2% of the cohort, and 72.9% of participants resided in rural areas. The mean duration of AR symptoms was slightly longer in Group B (4.8±2.3 years vs 3.9±2.1 years, p=0.17), though not statistically significant.

The seasonal distribution and frequencies of individual symptoms are presented in Table 2. Sneezing and nasal itching were significantly more prevalent in Group A (p=0.01 and p=0.03, respectively), whereas rhinorrhoea and nasal obstruction dominated in Group B (p=0.02 each). Ocular symptoms were reported by 58.3% overall and were comparable between groups. When symptom severity was analysed using the TNSS (Table 5), Group A recorded significantly higher mean scores for sneezing (2.4±0.6 vs 1.8±0.7, p<0.001) and nasal itching (2.2±0.7 vs 1.7±0.8, p=0.02). In contrast, Group B had significantly higher mean scores for rhinorrhoea (2.5±0.6 vs 2.1±0.8, p=0.04) and nasal obstruction (2.6±0.5 vs 1.9±0.9, p=0.002). The total TNSS was not significantly different between groups (8.6±1.9 vs 8.5±1.7, p=0.81), indicating a comparable overall disease severity but with divergent symptom profiles. These seasonal contrasts are illustrated in the bar chart (Figure 1).

Table 1: Demographic and Baseline Characteristics of the Study Population (N=48)

*Independent t-test; †Chi-square test. SD: standard deviation.

Table 2: Frequency of Individual Symptoms by Monsoonal Period

*Chi-square test.

[Figure 1: Bar chart comparing mean individual nasal symptom scores between Group A (July–September) and Group B (October–December). Error bars represent standard deviation. Sneezing and nasal itching are significantly higher in Group A, while rhinorrhoea and nasal obstruction are significantly higher in Group B.]

ARIA classification revealed a seasonal shift in disease persistence (Table 3). Persistent AR was more frequent in Group B (50.0%) than in Group A (25.0%), a difference that approached but did not reach statistical significance (p=0.07). The proportion of moderate-severe cases was similarly high in both groups (79.2% vs 75.0%, p=0.73). The overall distribution of ARIA classes in the entire cohort is depicted in the pie chart (Figure 2).

Table 3: ARIA Classification of Allergic Rhinitis by Season

*Chi-square test.

[Figure 2: Pie chart showing the distribution of ARIA classification in the overall study population (N=48). Intermittent AR accounted for 62.5% (n=30), persistent AR for 37.5% (n=18). Mild AR was observed in 22.9% (n=11) and moderate-severe in 77.1% (n=37).]

Allergen sensitisation patterns, determined by skin prick testing, exhibited a clear seasonal dichotomy (Table 4). During the southwest monsoon (Group A), pollen sensitisation dominated, with Parthenium hysterophorus (70.8%), Prosopis juliflora (62.5%), and Cynodon dactylon (54.2%) being the most frequent sensitisers. In contrast, during the northeast monsoon (Group B), sensitisation to moulds and house dust mites increased markedly. Dermatophagoides pteronyssinus sensitisation rose from 29.2% to 66.7% (p=0.009), Cladosporium herbarum from 16.7% to 50.0% (p=0.01), and Aspergillus fumigatus from 20.8% to 54.2% (p=0.02). Sensitisation to Alternaria alternata also showed a significant seasonal increase.

Table 4: Allergen Sensitisation Patterns by Skin Prick Test in Two Seasons

*Chi-square test. Only allergens with >15% sensitisation in either group are shown.

Table 5: Comparison of Mean Total Nasal Symptom Score (TNSS) and Individual Scores Between Seasons

*Independent t-test. SD: standard deviation.

This prospective study, conducted in a semi-urban tertiary care hospital in Tamil Nadu, demonstrates that the clinical presentation of allergic rhinitis undergoes a significant seasonal metamorphosis corresponding to the two monsoonal phases. During the southwest monsoon (July–September), patients predominantly presented with sneezing paroxysms and nasal itching, whereas the northeast monsoon period (October–December) was characterised by a shift toward nasal obstruction and profuse rhinorrhoea. This dichotomy was not accompanied by a significant difference in overall TNSS, suggesting that total disease severity remains stable while the symptom complex reconfigures itself in response to changing environmental allergen exposures. These findings align with the aerobiological hypothesis that warm, windy conditions during the early monsoon disperse large quantities of pollen grains, triggering histamine-mediated sneeze and itch reflexes, while the damp, humid conditions of the later monsoon foster fungal spore proliferation and house dust mite overgrowth, leading to a more congestive inflammatory phenotype [10,11]. The skin prick test results provide a biological substrate for this symptom shift. Sensitisation to weed pollens, particularly Parthenium hysterophorus and Prosopis juliflora, was significantly more frequent in the southwest monsoon group. These are well-known aeroallergens in India, with their peak airborne concentrations coinciding with the flowering season spurred by the first rains [7,12]. The decline in pollen sensitisation during the northeast monsoon, concomitant with a sharp rise in sensitisation to indoor perennial allergens Dermatophagoides pteronyssinus, Cladosporium, Aspergillus, and Alternaria mirrors the increased relative humidity and reduced ventilation typical of the season, which create microenvironments conducive to mite and mould growth [13,14]. The observed increase in D. pteronyssinus positivity from 29.2% to 66.7% is particularly striking and consistent with literature from eastern India, where mite sensitisation dominates during the post-monsoon and winter months [15,16]. These findings underscore the dynamic nature of allergic sensitisation in tropical climates and caution against a one-time allergy test divorced from the seasonal context. The ARIA classification data further support the seasonal influence on disease persistence. Although the majority of patients in both groups were classified as moderate-severe, persistent AR was twice as common during the northeast monsoon (50.0% vs 25.0%). This trend, though not reaching statistical significance (p=0.07), may reflect the prolonged indoor exposure to perennial allergens such as mites and moulds during the wetter months, converting what might be intermittent pollen-driven disease into a more sustained inflammatory state [17,18]. This observation has direct therapeutic implications: patients presenting in the October–December window may benefit from more prolonged courses of intranasal corticosteroids and consideration of mite-impermeable bedding covers, whereas those seen in July–September might be managed effectively with short-term antihistamines and pollen avoidance measures. Our results are in agreement with studies from Shanghai and other subtropical locations that have documented seasonal augmentation of perennial AR symptoms due to superimposed mould and mite exposure [19,20]. The integration of a simple, reproducible outcome measure such as the TNSS into the outpatient workflow proved feasible and clinically informative. By dissecting the composite score, we were able to detect statistically significant and clinically meaningful inter-season differences even with a modest sample size. The high overall TNSS in both groups (8.6 vs 8.5) indicates a substantial symptom burden, yet the differential symptom drivers offer an opportunity for personalised treatment. For example, an antihistamine with a prominent anti-pruritic effect might be preferred in the southwest monsoon, whereas a decongestant or leukotriene receptor antagonist could be a rational add-on in the northeast monsoon. Such seasonal tailoring of pharmacotherapy, guided by local aerobiological knowledge, represents a pragmatic approach to precision medicine in resource-limited settings where sophisticated molecular allergy diagnostics are not readily accessible. Finally, this study contributes to the sparse body of evidence characterising allergic rhinitis in the central Tamil Nadu region. Existing Indian literature has largely focused on metropolitan cities in the north or coastal cities such as Chennai and Puducherry [8,9]. Perambalur, with its agrarian landscape and distinct crop cycles, presents a unique exposure milieu. The high sensitisation rates to Parthenium (70.8% in Group A) and to multiple moulds in Group B highlight the need for region-specific allergen panels and the potential role of agricultural practices in driving allergic disease. Incorporating these seasonal patterns into public health initiatives, such as issuing mold spore alerts or pollen forecasts, could empower patients to implement timely environmental controls. Limitations of the Study This study has several limitations that warrant consideration. First, the sample size of 48, while statistically adequate for detecting moderate-to-large effect sizes in symptom scores, may have been underpowered to detect smaller differences in categorical outcomes such as the distribution of ARIA classes; the borderline p-value for persistent AR (p=0.07) suggests that a larger sample might have confirmed a significant seasonal influence. Second, the single-centre design based in one tertiary care hospital in Perambalur limits the generalisability of the findings to other regions of Tamil Nadu, particularly coastal or high-altitude areas where aerobiological profiles differ. Third, aeroallergen exposure was inferred from sensitisation profiles rather than direct ambient sampling; concurrent aerobiological monitoring with pollen and spore traps was not performed due to logistical constraints, and thus the temporal relationship between environmental allergen levels and clinical presentation remains presumptive. Fourth, we did not assess indoor environmental factors such as home dampness, use of air conditioning, or pet ownership, which could have confounded the seasonal association with mould and mite sensitisation. Finally, the six-month study period captured only the second half of the calendar year; a full twelve-month surveillance would be required to characterise the pre-monsoon summer and winter seasons, potentially revealing additional phenological shifts. Acknowledgment The authors express sincere gratitude to the administration of Dhanalakshmi Srinivasan Institute of Medical Sciences and Hospital, Perambalur, for providing the necessary infrastructure and institutional support. We thank the nursing staff and technicians of the ENT outpatient department and allergy testing laboratory for their assistance in patient recruitment and skin prick testing. Finally, we are deeply grateful to all the patients who participated in the study, without whom this research would not have been possible.

This study provides compelling evidence that the clinical expression of allergic rhinitis in the Perambalur region of Tamil Nadu undergoes a distinct seasonal oscillation between the southwest and northeast monsoons. The southwest monsoon is characterised by a pollen-predominant picture with sneezing and nasal itching as the dominant complaints, while the northeast monsoon heralds a shift towards a congestive, rhinorrhoeic phenotype driven by sensitisation to house dust mites and moulds. These findings highlight that a single cross-sectional assessment of AR, if not temporally contextualised, may miss an entire spectrum of allergic triggers and result in suboptimal management. Routine clinical practice in similar tropical settings should incorporate a detailed seasonal history and, whenever feasible, perform allergy testing during the period when symptoms are most pronounced, to capture the most relevant sensitisers.

Looking ahead, there is a pressing need for longitudinal, year-round studies that combine clinical phenotyping with continuous aerobiological monitoring in various microclimatic zones of Tamil Nadu. Such research would enable the construction of regional pollen and fungal spore calendars, which could be integrated into digital health platforms to deliver real-time allergen forecasts and personalised preventive advice. Furthermore, the observed seasonal modulation in symptoms and allergen sensitivity supports the concept of “seasonal immunotherapy” or adjuvant strategies timed to preempt the dominant allergen season. By embracing the rhythm of the monsoons, clinicians can transform a generic diagnosis of allergic rhinitis into a seasonally intelligent, patient-specific therapeutic plan, ultimately improving the quality of life for millions in the region.