While shampoo often does not come with an expiration date, it generally keeps for anywhere from one to three years. Although expired shampoo is not dangerous to use, it is less effective than fresh shampoo.
Just because a shampoo does not include an expiration date does not mean that it lasts forever. A sure sign that shampoo is ready for the trash bin is a significant change in color or consistency. Additionally, changes in the smell of the shampoo may also indicate that it has gone bad. Tossing shampoo when it starts to turn bad and using a fresh bottle helps to keep hair looking and feeling healthy.