  Quantum spin systems can break time reversal symmetry by developing
spontaneous magnetization or spin chirality. However, collinear magnets and
chiral spin states are invariant under different symmetries, implying that the
order parameter of one phase vanishes in the other. We show how to construct
one-dimensional anisotropic spin models that exhibit a "Landau-forbidden"
continuous phase transition between such states. As a concrete example, we
focus on a zigzag chain with bond-dependent exchange and six-spin interactions.
Using a combination of exact solutions, effective field theories, and numerical
simulations, we show that the transition between the chiral and magnetic phases
has an emergent U(1) symmetry. The excitations governing the transition from
the chiral phase can be pictured as mobile defects in a $\mathbb Z_2$ flux
configuration which bind fermionic modes. We briefly discuss extensions to two
dimensions and analogies with deconfined quantum criticality. Our results
suggest new prospects for unconventional phase transitions involving chiral
spin states.
