Mixing in stars and the evolution of the 3He abundance

We first recall the observational and theoretical facts that constitute the so-called He-3 problem. We then review the chemical anomalies that could be related to the destruction of He-3 in red giants stars. We show how a simple consistent mechanism can lead to the destruction of He-3 in low mass stars and simultaneously account for the low C-12/C-13 ratios and low lithium abundances observed in giant stars of different populations. This process should both naturally account for the recent measurements of He-3/H in galactic HII regions and allow for high values of He-3 observed in some planetary nebulae. We propose a simple statistical estimation of the fraction of stars that may be affected by this process.