Renormalization of the current masses of light quarks by instantons is considered. It is shown that the entire low-energy current mass of the $u$ quark can be generated by this nonperturbative mass renormalization. In this case, the absence of $\mathrm{CP}$ nonconservation in the strong interactions is an automatic consequence.

• Received 10 March 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.794