How do you tell if a bath bomb is expired?

What Is a Bath Bomb and What Is a Bath Bomb Made Of?

A bath bomb is made using a good balance of bicarbonates and a weak acid. When placed in water, the ingredients of a bath bomb will react. The result is a bubble and fizz effect when connecting with bath water. 

This effect is due to the release of carbon dioxide and sodium citrate, creating a chemical reaction. As the bubble and fizz effect takes place, the bath bomb emits sensational scents and colours. This is because when the bath bomb dissolves, it begins to break apart. Here is where the good stuff is released.

The result is a spectacular display in the bathtub. But, ultimately bath bombs release several emollients that are softening for the skin. So, bath bombs are one of the most luxurious bath time treats.

Composition

Bath bombs' primary ingredients are a weak acid and a bicarbonate base. These are unreactive when dry, but react vigorously when dissolved in water to produce their characteristic fizzing over a period of several minutes. This is an acid–base reaction that involves conversion of citric acid and sodium bicarbonate to monosodium citrate and carbon dioxide:

C₅H₇O₅CO₂H _(aq.) + NaHCO_{3 (aq.)} → C₅H₇O₅CO₂⁻Na⁺_(aq.) + H₂O_(l) + CO_{2 (g)}

The other ingredients in bath bombs can vary considerably. However, most have scented ingredients as well as dye to impart a pleasant fragrance and color to bathwater. Lathering agents, such as sodium lauryl sulfate, are also often added to create bubble foams.

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.

How can you tell if a bath bomb has expired?

Smells: Old bath bombs that have passed their expiration date might begin to have a chemical smell or have that rancid smell. If it has a weird smell different from its natural fragrance, then you should halt using it.
No Fizz: An old bath bomb will lose its fizz as its ingredients like baking soda and citric acid constantly lose a bit of their effectiveness as time passes and would not have the same reaction. The constituents mentioned are the real reason a bath bomb fizzes. If your bath bomb doesn't have any fizz in it, it is likely that it doesn't work as well as it should. So, don't use it to avoid being disappointed.
Discoloration: With time, bath bombs are known to change their shade or fade in color. The more faded your bath bomb looks, the more you are certain it has gone past its expiry date. It is important to note that you should not use a bath bomb that has really faded as it can irritate your skin.
Mold: Can mold grow on bath bombs? The short answer is yes. Mold growing on your bath bomb is a great sign that it is way over its expiry date. Most people don't know that it is dangerous to use bath bombs with mold on them. Bath bombs with natural ingredients like milk, butter, and oatmeal are more likely to be moldy. This can also happen if your bath bomb has been exposed to oxygen, mold spores, or water.

Can I still use an expired bath bomb?

A bath bomb is a product that contains foam agents or fragrant ingredients for a luxurious bathing experience. While you didn't mention a specific expiration date, generally, the ingredients in a bath bomb may lose their effectiveness or diminish over time.
If your bath bomb has expired, I would recommend not using it as expired products may lose their intended effects and could potentially harbor bacteria. Additionally, the bath bomb may become dry, hardened, or lose its fragrance, resulting in a less enjoyable experience.