Castile soap is alkaline, so you should not mix it with acids like lemon juice and vinegar. The mixture could leave residue on household surfaces, your skin, laundry, or your hair.

If you have hard water, a mixture of castile soap and water can leave behind residue.

Using a castile soap cleanser on a shiny or hard surface? It may leave a salty deposit behind even though it cleans the surface. Lemon or vinegar can cut the leftover salt deposit, so you may want to spray on a vinegar/water mixture afterward.

Common Mistakes When Adding Scents

Don’t add scent to the base and shake-you will end up with foam for the next day or so until it settles, and the
fragrance will likely not incorporate.

Don’t add extra base oils to the soap. Since the nature of true soap is to break down oils, if you add any extra oils to the base, the soap tries to break down this oil and, ends up cannibalizing itself.

Don’t add salt to thicken. This base has no Sulfate type of ingredients, so it will not thicken up with salt. Liquid glycerin does not make this base better, it only makes it watery due to glycerin being a form of alcohol. 

Don’t use a stick blender when incorporating ingredients, you’ll only end up with pretty foam that smells good. It’s best to fold additives in by hand.

Don’t add organic ingredients unless you know about preservation techniques (for example, fresh apple rinds may look nice for about a week before they mold).

Innovations: Add herbal teas after thickening with fragrance. Filter out any particles. Add Aloe Vera for extra skin benefits. Add glycerin soap scraps (melt them first) – they will create a neat gel, fun kid soaps, or shaving gel.