Background: Air pollution is a global problem with PM2.5 being one of the major pollutants causing many diseases. The concentrations of PM2.5 are found to exceed the World Health Organization (WHO) standards especially in lower middle-income countries (LMICs) that house around 40% of the global population. Materials and Methods Studies conducted globally in the past 5 years (2015–2019) on health effects of PM2.5 were systematically reviewed to understand the current research gaps. For this systematic search, Web of Science and PubMed were used to obtain 247 articles. Results Systematic review of these studies revealed that PM2.5 and other air pollutants have been found to be associated with increased mortality and morbidity due to respiratory, cardiovascular, cerebrovascular disorders and diabetes. However, most of the total studies (~ 69%) were carried out in the high-income countries (HICs) despite the fact that PM2.5 concentrations are higher in the LMICs (annual mean exposure (2011–2017) of 48.42 µg/m3) and lower in the HICs (annual mean exposure (2011– 2017) of 20.02 µg/m3). Therefore, the exposure response functions for mortality estimates associated with PM2.5 and developed using the exposure data from the HICs will not have predictive value in the LMICs. Furthermore, very few studies relate chemical components and source apportionment of PM2.5 to the associated toxicity. Conclusions More studies on morbidity and mortality associated with PM2.5 and its components are needed in LMICs for better estimation of the overall risks.