1/8 teaspoon of baking soda
1/4 teaspoon of water
Dissolve the baking soda into the water - the liquid should feel slippery, since sodium bicarbonate is a base - and apply directly to skin. Adjust quantities as necessary - you may need less, you may need more.
Since there's different "types" of water, you may need to adjust the recipe. If your water easily rinses away the "slimy" feel of sodium bicarbonate, you'll need to use more. If your water does not easily rinse it away, you'll need less.
Too much sodium bicarbonate will cause some skin irritation. It also needs to be dissolved sufficiently, because dry powdery baking soda can chafe skin just like sand.
By the way, the water solution will leave white stains on clothes or countertops wherever it drips and dries out, but it washes away easily. After all, another use of baking soda is as a cleanser!