It's cheap, abundant and all-natural. We use it for baking, cleaning and deodorizing. It has been called upon in the battle against global warming (see Can baking soda save the environment?) And apparently, it can also improve the complexion.
Baking soda, or sodium bicarbonate (NaHCO3), is a white, powdery substance. What makes it such a good exfoliant is the nature of its particles: They're hard enough to slough off dead cells, but fine enough to do it without irritating the skin. In this way, baking soda can be especially good for dry or sensitive skin, which does better with smaller exfoliating particles (oily skin can better handle harsher exfoliating methods).
To exfoliate sensitive skin with baking soda, add a teaspoon to your cleanser and massage it into your skin as usual. For more resilient skin, you can simply pour some baking soda into a container and add enough water to make a thick paste. Then gently massage it into your skin and rinse off. Baking soda is safe for both facial and body exfoliation.
Up next: a higher-tech method.