Our hair will last forever - in terms of its condition. The hair is in perfect condition at the first fitting, and for each refit thereafter. When a client decides to have new hair, it is not because the hair itself has gone dry or is less glossy. The main reason why clients choose to have new hair is because their own hair changes over time.
When you have hair fitted, it grows out with your own hair. When you then have it refitted, it is shifted up to the root again, but your own hair is longer than it was before.
Additionally, your own hair changes colour over time. Sometimes due to seasonal changes, or because the root area is not dyed as often and the underneath part becomes darker over time.
Eventually, new hair is needed to ensure the colour match is exact and the desired goal in terms of length is on point too.
Most clients who add a lot of length to begin with are able to refit the same hair for a year. For clients who don't add much length to begin with, it is less time.