The authors conducted a systematic review of the literature to understand the impact of air pollution on the hospitalization of multimorbid patients. They searched six databases using key terms such as "air pollution", "multimorbidity" and "hospital restrictions" and included studies in English on PM2.5, PM10, SO2, NO2, O3 and CO. They grouped 19 studies into four clinical groups: cardiovascular, respiratory, neurodegenerative and mental health, addiction and liver disease. PM2.5 was the most studied substance, but NO2 led to an increase in hospital visits after 2 days of exposure compared to 5 days for PM2.5. Factors such as temperature, demographics (age, gender), chronic conditions, and the "CADC" effect influence the likelihood of hospitalization. Exposure to pollutants increases the risk of hospital visits in multimorbid patients. Future research is needed on the CADC effect, especially in people from lower socioeconomic backgrounds. The review is registered under CRD42022369757 and follows PRISMA guidelines.