The simple answer is that our products have an expected shelf life of about 2.5 years. After that, you may begin to see changes in the way they look, smell or work.
That said, an older product may work perfectly fine if it has not been exposed to factors that age products faster, such as light or heat. The best thing to do is give it a try in an inconspicuous area first. If it seems to have lost its cleaning abilities, just empty the bottle and recycle it.