In a large bowl, combine the citric acid, Epsom salts, baking soda, and corn starch. Stir to combine.

Pour in the peppermint essential oil. You can cut it with a carrier oil like coconut oil if you wish. Stir to combine.

Add in food coloring or mica powders to color the foot soak bombs if you would like. Stir to distribute the coloring.

Try the squeeze test. Pick up a bit of the mixture and squeeze it in your hand. It should hold together. If it does not, add a bit of melted coconut oil or a few spritzes of witch hazel until it reaches the right consistency.