  At high gluon or string densities, gluons' saturation or the strong
interaction among strings, either forming colour ropes or giving rise to
string's percolation, induces a strong suppression in the particle
multiplicities produced at high energy. This suppression implies important
modifications on cosmic ray shower development. In particular, it is shown that
it affects the depth of maximum, the elongation rate, and the behaviour of the
number of muons at energies around 10^{17}-10^{18} eV. The existing cosmic ray
data point out in the same direction.
