These palm-size spheres are actually a mix of fizzy ingredients, salts, colorants, oils, and some surprises rose petals or glitter, as the case may be.
Cosmetic chemist Randy Schueller, editor of thebeautybrains.com, explains this.
In water, the sodium bicarbonate in the bomb reacts with the citric acid to release carbon dioxide gas.
This is no different from what happens when you drop an Alka-Seltzer tablet in a glass of water.
The bath bomb starts to break apart and as this happens, releasing with it the colorants, fragrances, and skin-conditioning ingredients, like salts and oils.
The combination turns your bath water a psychedelic blend of colors and scents your whole bathroom, but as far as your skin is concerned, they're essentially no different from adding a splash of bath oil or salt into the water.
"Bath bombs can add oils to a bath, and the oils are moisturizing," says Amy Wechsler, a dermatologist in New York City.
"On the other hand, some of the ingredients can be irritating, especially the fragrances and dyes." Not to mention picking glitter from sensitive regions".
So, for those who have skin that is sensitive, its advised to skip the bath bomb altogether.
At the end of the day, Bath bombs fall into the same category as baths themselves.
Its less about function and more about the sensory experience.
So unless you're concerned about irritants, enjoy your bombs!