Technically it suppose to protect you, but it forces viral evolution to favor more infective strains, masks are only limiting viral load - they don't eliminate it 100% so you evolve personal strains that will spread on smaller droplets and infect more people through masks. Just like vaccines and anti-biotics that kill 99.9% of the germs allow the remaining 0.1% to survive and thrive to become the next generation: E.g. flu "vaccine" forcing evolution of the virus in direction that evades current vaccine and stimulating production of more vaccines. Coronavirus infections works in similar way.