The titanium dioxide photocatalyst itself has a semi-permanent duration since it is stable and does not react, but it may lose effectiveness if undecomposable substances (inorganic material or too much organic dirt) adhere to the surface.

(In this case, it will recover by washing with water and then exposing to sunlight).

There may be cases where the resin that fixes the photocatalyst deteriorates or comes off resulting in the loss of the titanium dioxide. This why BLG uses one the best resin surface coating binder to work with its additive to create a permanent treatment that last for years to come.