What causes fizzing in bath bombs?

The “bomb” aspect of a bath bomb is the fizziness. But what’s going on in those spheres that make them so fizzy? Two of the key ingredients to a bath bomb are citric acid and sodium bicarbonate. You might also know sodium bicarbonate by its more common name, baking soda. These two ingredients are what cause the impressive and delightful fizz when the bath bomb enters the water.

When sodium bicarbonate (NaHCO3) comes in contact with water, the sodium (Na) molecules break off from the bicarbonate (HCO3). At the same time, the citric acid is dissolving, with a single hydrogen ion (H+) separating from the rest of the molecule. When the released hydrogen ion from the citric acid encounters the bicarbonate from the baking soda another reaction happens! This time, carbon dioxide (CO2) gas is released as one of the end products. The carbon dioxide forms bubbles in the soap and bath water, and rushes to the surface with a delightful fizz.

Now here’s a question for you! We explained how a hydrogen ion (H+) reacts with bicarbonate (HCO3) to create carbon dioxide (CO2). Can you guess what the other product of that reaction would be? Hint: you’d already be sitting in a bathtub full of it.

How to use a bath bomb?

Just follow the four-step guide below and you'll be on your way to luxurious relaxation. 
Step by step 
1, Fill your tub with water that's comfortable to the touch.  You should be able to dip your hand into the water and leave it there comfortably for up to 10 seconds. 
2, Make sure you don't fill your tub straight to the top—you could lose some of your beautiful bath bomb water when you get in. 
3, Drop in the handmade bath bomb of your dreams and enjoy the show.  Some have hidden sparkle, a blend of colors, gorgeous fragrance and more.  Watch the magic unfurl. 
4, Get in and enjoy!  Now's the perfect time to kick back, throw on a mask, put on a podcast and really take some time for yourself.

Do Bath Bombs Expire?

Bath bombs have a shelf life of about one year. A bath bomb will last only as long as its composite ingredient with the least shelf life. It is true that a bath bomb has a scent as sweet as an air freshener, but if it does expire, it will start to its scents as well as its good looks and effect.
If your bath bomb starts to smell bad, break up or grow mold, it is a sign that it has expired, and you should learn to throw them out at this point.