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Surgical masks do not provide protection in the level you need to block our other people’s. They block some but the gaps around the edges are too large. Everyone is supposed to wear one becuase it looks like most propagate asymptomatic and spread it. Wearing a mask stops that
Think of a basic diffusion equation. Swapping the sign on the pressure gradient is the exact same as swapping the sign on time. So exhalation is just time-reversed inhalation. Air will take the same routes both in and out of the mask.