Recent reports have suggested that an exponential dependence of failure time on applied stress provides a more fundamental description of fatigue, but the power law is usually used to assess the long‐term mechanical reliability of lightguide fibers. A consequence of the exponential expression is a linear dependence of applied stress and activation energy. This study applies the exponential law to all temperature‐dependent fatigue data for lightguide fibers reported in the literature. The results show consistency with the prediction of the exponential express