Abstract: We included 14 studies (747 participants). The studies included children (seven studies, 499 participants) and adults (seven studies, 248 participants). No studies reported outcomes beyond three months follow-up. Saline volumes ranged from 'very low' to 'high' volume. Where stated, studies used either hypertonic or isotonic saline solution. Nasal saline versus no saline treatment All seven studies (112 adults; 332 children) evaluating this comparison used different scoring systems for patient-reported disease severity, so we pooled the data using the standardised mean difference (SMD). Saline irrigation may improve patient-reported disease severity compared with no saline at up to four weeks (SMD -1.32, 95% confidence interval (CI) -1.84 to -0.81; 407 participants; 6 studies; low quality) and between four weeks and three months (SMD -1.44, 95% CI -2.39 to -0.48; 167 participants; 5 studies; low quality). Although the evidence was low quality the SMD values at both time points are considered large effect sizes. Subgroup analysis showed the improvement in both adults and children. Subgroup analyses for volume and tonicity were inconclusive due to heterogeneity. Two studies reported methods for recording adverse effects and five studies mentioned them. Two studies (240 children) reported no adverse effects (epistaxis or local discomfort) in either group and three only reported no adverse effects in the saline group. One study (48 children) reported disease-specific HRQL using a modified RCQ-36 scale. It was uncertain whether there was a difference between the groups at any of the specified time points (very low quality). No other secondary outcomes were reported. Nasal saline versus no saline with adjuvant use of intranasal steroids or oral antihistamines Three studies (40 adults; 79 children) compared saline with intranasal steroids versus intranasal steroids alone; one study (14 adults) compared saline with oral antihistamines versus oral antihistamines alone. It is uncertain if there is a difference in patient-reported disease severity at up to four weeks (SMD -0.60, 95% CI -1.34 to 0.15; 32 participants; 2 studies; very low quality) or from four weeks to three months (SMD -0.32, 95% CI -0.85 to 0.21; 58 participants; 2 studies; very low quality). Although none of the studies reported methods for recording adverse effects, three mentioned them: one study (40 adults; adjuvant intranasal steroids) reported no adverse effects (epistaxis or local discomfort) in either group; the other two only reported no adverse effects in the saline group. It is uncertain if saline irrigation in addition to pharmacological treatment improved disease-specific HRQL at four weeks to three months, compared with pharmacological treatment alone (SMD -1.26, 95% CI -2.47 to -0.05; 54 participants; 2 studies; very low quality). No other secondary outcomes were reported. Nasal saline versus intranasal steroids It is uncertain if there was a difference in patient-reported disease severity between nasal saline and intranasal steroids at up to four weeks (MD 1.06, 95% CI -1.65 to 3.77; 14 participants; 1 study), or between four weeks and three months (SMD 1.26, 95% CI -0.92 to 3.43; 97 participants; 3 studies), or indisease-specific HRQL between four weeks and three months (SMD 0.01, 95% CI -0.73 to 0.75; 83 participants; 2 studies). Only one study reported methods for recording adverse effects although three studies mentioned them. One (21 participants) reported two withdrawals due to adverse effects but did not describe these or state which group. Three studies reported no adverse effects (epistaxis or local discomfort) with saline, although one study reported that 27% of participants experienced local discomfort with steroid use. No other secondary outcomes were reported. Saline irrigation may reduce patient-reported disease severity compared with no saline irrigation at up to three months in both adults and children with allergic rhinitis, with no reported adverse effects. No data were available for any outcomes beyond three months. The overall quality of evidence was low or very low. The included studies were generally small and used a range of different outcome measures to report disease severity scores, with unclear validation. This review did not include direct comparisons of saline types (e.g. different volume, tonicity). Since saline irrigation could provide a cheap, safe and acceptable alternative to intranasal steroids and antihistamines further high-quality, adequately powered research in this area is warranted.

Plain-language summary: We found 14 studies with a total of 747 participants (260 adults; 487 children). The volume of saline used in the studies varied: five studies used 'very low' volumes (nasal sprays providing less than 5 mL saline per nostril per application), two studies used low-volume (between 5 and 59 mL saline per nostril per application introduced with a syringe) and four studies used high-volume solutions (more than 60 mL per nostril per application). Eight studies used hypertonic saline, five used isotonic saline and three studies did not provide this information. Two studies used two different types of saline solutions. Seven studies did not say how they were funded. The other seven were funded either by the investigators' department or research grants from regional or national government. No studies were funded by pharmaceutical companies. Nasal saline irrigation compared with no saline irrigation Nasal saline irrigation may have benefits in both adults and children in relieving the symptoms of allergic rhinitis compared to no saline irrigation and it is unlikely to be associated with adverse effects. It is not possible to tell from this review whether there is a difference between the different volumes and concentrations of saline solution. Adding nasal saline irrigation onto 'pharmacological' allergic rhinitis treatment It is uncertain whether adding nasal saline irrigation to pharmacological treatment (intranasal steroids or oral antihistamines) helps to improve the symptoms of allergic rhinitis compared to using pharmacological treatments alone. The use of nasal saline irrigation is unlikely to be associated with adverse effects. Nasal saline irrigation compared to 'pharmacological' allergic rhinitis treatment There is not enough evidence to know whether nasal saline irrigation is better, worse or the same as using intranasal steroids. No studies reporting the outcomes we were interested in compared nasal saline irrigation with oral antihistamines. The overall quality of evidence for nasal saline irrigation compared with no saline treatment was eitherlow quality (our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect) or very low quality (we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect). This was because the studies were mostly very small and used different methods to measure the same outcome. Since saline irrigation could provide a cheap, safe and acceptable alternative to intranasal steroids and antihistamines further high-quality studies are needed.