Before you start sniffing every bottle in your house, here are three dead giveaways. Smell it: if it doesn’t smell strongly of alcohol (or whatever the active ingredient is), it’s likely weak. Look at it: if it’s cloudy, separated, or has floaters—bye bye. Feel it: if the gel feels watery or runnier than when you bought it, evaporation has taken its toll.
I once ignored a bottle that was perfectly clear but smelled like cheap perfume. Wanna guess what happened? I sanitized, then later that day touched my eye. Guess who got a stinging, red eye? This guy. The solution had probably gone acidic or something. Not fun.
