Background: The hypertension risk in the co-occurrence of allergic diseases remains largely unknown. Objective: We aimed to investigate the association between allergic diseases co-occurrence pattern and hypertension morbidity and mortality, and to evaluate additive interaction effects between allergic diseases. Methods: A nationally representative population from the U.S. National Health Interview Survey 2012 was enrolled. Hypertension and five specific allergic diseases, including asthma, allergic rhinitis (AR), food allergy (FA), eczema, and other allergy (OA), were determined. Hypertension mortality was identified until December 31, 2019. We evaluated additive interaction effects between two allergic diseases on hypertension risk: relative excess risk due to interaction (RERI) and attributable proportion of joint effect due to interaction (AP) (shown as percentages) were calculated. For modifiable lifestyle factors with significant heterogeneity in the subgroups, we examined the effect modification. Results: Totally, 34,392 participants were enrolled. Four co-occurrence patterns of two allergic diseases were associated with an increased risk of hypertension, including AR + FA (odds ratio [OR] 2.25 [95% confidence interval {CI}, 1.52‐3.35]), eczema + OA (OR 1.94 [95% CI, 1.14‐3.30]), AR + eczema (OR 1.76 [95% CI, 1.18‐2.64]), asthma + AR (OR 1.67 [95% CI, 1.33‐2.08]). Five co-occurrence patterns of three allergic diseases were associated with increased risk of hypertension. Additive interactions were seen in AR + FA (RERI, 0.65; AP, 29%), eczema + OA (RERI, 0.43; AP, 22%), AR + eczema (RERI, 0.21; AP, 12%), and asthma + AR (RERI, 0.05; AP, 3%). The significant association between asthma + FA and hypertension was only seen among participants with a body mass index (BMI) ≥ 30 kg/m2 (p = 0.021). With a median follow-up of 7.5 years, one co-occurrence pattern of asthma + FA showed a significant increased risk of hypertension mortality (hazard ratio 4.32, 95% CI: 1.52‐12.23), with an additive interaction was observed (RERI, 2.33; AP, 52%). Conclusion: We identified several allergic diseases co-occurrence patterns with a significantly increased risk of hypertension morbidity and mortality. Potential biologic additive effect among allergic diseases and effect modification of BMI was found. Precision primary prevention of hypertension is necessary for patients with co-occurring allergic diseases.