Yes, hair colors do expire. Most hair dyes have expiration dates written or stamped in the box but if you cannot find it, checking the manufacturer’s website may be a good idea, or even calling their customer service. An unopened box can still be used for up to three years. But once it is opened and exposed to air, you may just want to throw it out in the garbage. It is safer to spend a few dollars for a new box than take chances. Though it is thought to only affect the effectiveness of the color, but you may also consider scalp irritation as a possibility.