Association between asthma, allergic rhinitis, atopic dermatitis, and dental caries: evidence from systematic review with meta-analysis and Mendelian randomisation investigation

Background: Allergic diseases and dental caries share overlapping epidemiological trends and risk factors, compromising the patients' quality of life and increasing health care costs. We aimed to explore the associations and potential causal relationships between allergic diseases (asthma, allergic rhinitis, and atopic dermatitis) and the presence/severity of dental caries. Methods: We conducted a systematic review and meta-analysis by searching PubMed, Embase, and the Cochrane Library studies published up to 16 June 2025 reporting dental caries outcomes in relation to asthma, allergic rhinitis, or atopic dermatitis. We calculated pooled odds ratios (ORs) and standardised mean differences (SMDs) using random-effects models and utilised meta-regression to investigate heterogeneity. Then, we performed a two-sample Mendelian randomisation (MR) analysis based on genome-wide association study data to assess causal relationships, employing inverse-variance weighted (IVW) and other MR methods. Results: We included 60 studies encompassing 343 975 participants across 22 countries/regions. Asthma (OR = 1.44; 95% CI = 1.17, 1.76) and atopic dermatitis (OR = 1.09; 95% CI = 1.01, 1.17) were associated with an increased risk of dental caries, while allergic rhinitis was not (OR = 1.01; 95% CI = 0.86, 1.18). Asthma and atopic dermatitis patients had higher decayed, missing, and filled teeth for permanent dentition (DMFT) scores, with SMDs of 0.92 (95% CI = 0.32, 1.52) and 0.06 (95% CI = -0.02, 0.14). We also found higher decayed, missing, and filled surfaces for permanent dentition (DMFS) and decayed, extracted, and filled surfaces for primary dentition (defs/dfs) scores in allergic patients, while dmft/dft and the plaque index scores did not show statistically significant associations, with SMDs of 0.17 (95% CI = -0.60, 0.93) and 1.78 (95% CI = -1.47, 5.03), respectively. The MR analysis confirmed a potential causal link for asthma (IVW OR = 1.09; 95% CI = 1.02, 1.17) and a non-significant trend for atopic dermatitis (OR = 1.05; 95% CI = 0.99, 1.11). Conclusions: Our analysis showed that asthma and atopic dermatitis could be associated with an increased risk and severity of dental caries, while allergic rhinitis is not. Clinical practitioners could consider adopting an integrated prevention strategy that addresses the comorbidity between oral health and allergic diseases. Registration: PROSPERO: CRD420251103903.