These molecules oxidize to form sulfates, which condense with water vapor in the air to form a blanket of fine particles that impair visibility and cause severe lung damage.
Well, a lot of rocks on Mars are full of iron, and when they're exposed to the great outdoors, they 'oxidize' and turn reddish, the same way an old bike left out in the yard gets all rusty.
The zinc oxidizes, which means it loses electrons, which are, in turn, gained by the ions in the water in a process called reduction, producing hydrogen gas.
The trapped sebum and dead skin cells become oxidized, which turns the surface of the clogged material into a dark color, kind of like how silver tarnishes.