Shampoo and conditioner
Because the FDA doesn’t require companies to put expiration dates on shampoo and conditioner, it can be hard to tell how long we should keep using it. These bathroom products do have a shelf life, though, and using expired shampoos can lead to horrible effects.
You should only keep your bottles around in the shower for 18 months. After this time bacteria can spread within the bottle and then infect the scalp while you wash, which is sort of the opposite idea of washing your hair. It’s best to purchase a new bottle the next time you go to the grocery store.