How Do Bath Bombs Work?
by Jonny Parker
Posted on Jul 31, 2018
Bath bombs are hard-packed mixtures of dry ingredients which effervesce when wet. They are used to add essential oils, scent, bubbles or color to bathwater. Bath bombs came to the world in 1989 by Mo Constantine, who happens to be one of the founders of Lush.
Bath bombs contain a certain chemical such as sodium bicarbonate, more commonly known as baking soda, as the main ingredient. Without baking soda, there is no bath bomb.
Most people out there know that baking soda alone isn’t good for your skin because it’s a base, with high pH levels. High pH, which can be alkaline or basic, products irritate the skin’s acid mantle, which is what protects the body's living tissue from the environment, mainly bacteria.
But there is nothing to be alarmed about as the second main ingredient in a bath bomb is a solid acid, such as citric acid or tartaric acid, more commonly known as cream of tartar. This lowers the pH levels once it begins to react with the baking soda when water is added to the mix. So be sure to have your proportions on point or as close to as possible so that the final pH should is reasonably neutral. Once the water begins to dissolve the acid and baking soda, which allows the ingredients to mix at a smaller level, nothing really happens.
Other than neutralization, the acid plus the base reaction it has with sodium carbonate and produces small bubbles of carbon dioxide gas, which is when the fizzing begins:
- Citric acid + sodium bicarbonate → sodium citrate + water + carbon dioxide
- C6H8O7(s) + 2NaHCO3(s) → Na2C6H6O7(aq) + 2H2O(l) + 2CO2(g)
This is very similar to the reaction that is most commonly used in volcano science projects in order to create the foaming “lava” reaction, which is usually vinegar instead of the acid.
Bath bombs also contain fragrance, essential oils, colors and sometimes eco-friendly glitter. The fizzing helps the bath bomb to disperse quicker, mixed with the hot bath water, the fizzing spreads the colors and scent faster and makes the bath tub look like a beautiful art piece while also making the entire bathroom smell amazing.
Bath bombs slowly absorb the water in the air, which uses up the acid and sodium carbonate (baking soda) and releases carbon dioxide prematurely. This is what causes bath bombs to get less fizzy as they get old! So make sure you keep your bath bombs in a dry, air tight if possible, place until you’re ready to use them.