<p>Evidence exists for the airborne transmission of contagious pathogens such as SARS-CoV-2, influenza A virus and <i>Mycobacterium</i> <i>tuberculosis</i> in indoor environments. These pathogens are carried in the respiratory droplets and transmitted through airborne route to infect individuals. An important element in risk assessment for pathogenic bioaerosol exposure is a determination of the inhaled deposited dose rate – the number of deposited pathogenic particles per minute – received by each respiratory region and the fractional reduction of dose rate by different material facemasks. This paper presents an aerosol physics-based modeling framework to estimate the fractional reduction of regional dose rate in diverse indoor healthcare environments. The fractional reduction of dose rate is a useful metric to evaluate the facemask effectiveness in reducing the inhaled dose rate. Data extraction of pathogenic bioaerosol size distributions and size-dependent facemask filtration efficiency curve combined with deposition fraction model become the baseline to calculate the fractional reduction of dose rate by 10 different facemasks. Facemask leakage is also considered for the realistic representation of its impact on reduction fraction as current studies focus on mask material filtration efficiency. This analysis considers how the fractional reduction of dose rate is influenced by the pathogenic bioaerosol size distribution, age-dependent respiratory parameters, age-specific deposition fraction, facemask filtration efficiency and mask leakage. Different factors drove variations in the reduction fraction of various sized-pathogenic bioaerosols received by each respiratory region for each age group. This framework can be a useful tool for decision-makers in evaluating the mask’s effectiveness in reducing deposition of pathogenic bioaerosols.</p>