Physically, the probability that an aerosolized particle enters your body is lower with a mask than without one, as at least some airflow will go through the mask and carry particles onto the mask surface. How much lower, of course, is difficult to predict.

It’s worth noting in this context that masks have been shown to protect the wearer, not just to prevent the wearer transmitting viruses. See e.g. https://www.cdc.gov/mmwr/volumes/71/wr/mm7106e1.htm