According to Gina Rivera, founder of Phenix Salon Suites, expired shampoo can have a direct result to your scalp, leading to itching and irritation. "Expired products undergo a chemical change," Rivera explained to Healthline, "which means they're no longer effective at a high level." And if the shampoo you're using is organic or sulfate-free, this can often result in a shorter shelf life. "This is due to the lack of preservatives and the addition of more health-based ingredients," she said.

If you don't experience irritation from the expired shampoo, you will notice that the result it once had on your hair will have all but disappeared. Essentially, you're putting something in your hair that is literally doing nothing to it. And on the rare occasion, according to Style Craze, there could also be some "bacterial or fungal growth invisible to the eye" going on in there, which can also result in irritation on your scalp and skin. Yikes!