In a large bowl, whisk together the baking soda, citric acid, epsom salts, and corn starch.
In a small bowl, mix the avocado oil, water, and essential oils.
Slowly drizzle the liquid mixture into the dry ingredients, stirring constantly. Add a little bit at a time to avoid early fizzing.
If needed, lightly mist with witch hazel using a spray bottle until the mixture holds together when squeezed (similar to wet sand).
Firmly pack the bath bomb mixture into your molds, pressing tightly.
Let the bath bombs dry in the molds or on parchment paper for 24 hours.
Once dry, carefully remove from the molds and store in an airtight container or a glass jar.
