  Mass-loss rates during the red supergiant phase are very poorly constrained
from an observational or theoretical point of view. However, they can be very
high, and make a massive star lose a lot of mass during this phase, influencing
considerably the final evolution of the star: will it end as a red supergiant?
Will it evolve bluewards by removing its hydrogen-rich envelope? In this paper,
we briefly summarise the effects of this mass loss and of the related
uncertainties, particularly on the population of blue supergiant stars.
