A bath bomb is a palm-size ball or disc, generally made of baking soda, citric acid, oils, and dyes that dissolve in water. And it can transform a simple soak into the highlight of one’s day, calming nerves and softening skin while entertaining bathers with fantastic fizz, soothing scents, and captivating colors. After soaking in data from 49 on-the-record baths involving bath bombs from 16 different brands, we’re certain...