  We consider the collinear limit of QCD amplitudes at one-loop order, and
their factorization properties directly in colour space. These results apply to
the multiple collinear limit of an arbitrary number of QCD partons, and are a
basic ingredient in many higher-order computations. In particular, we discuss
the triple collinear limit and its relation to flavour asymmetries in the QCD
evolution of parton densities at three loops. As a phenomenological consequence
of this new effect, and of the fact that the nucleon has non-vanishing quark
valence densities, we study the perturbative generation of a
strange--antistrange asymmetry $s(x)-\bar{s}(x)$ in the nucleon's sea.
