The Lyman alpha emission line might be a very powerful tool to study the history of star formation in the Universe, but it is so much affected by resonance scattering in neutral gas that using it without propoer correction might be misleading. In this contribution we will present our studies to derive the Lyman alpha escape fraction in the Local Universe and at redshift around 2, by analyzing simultaneously H alpha and Lyman alpha observations. We will also discuss the evolution of the escape fraction along the history of the Universe, derived by conmparing luminosity functions of various star formation rate tracers at different ages.