The Carbon-Nitrogen-Oxygen Cycle

Another cycle that can convert Hydrogen into Helium is the Carbon-Nitrogen-Oxygen Cycle or CNO cycle. For this cycle to operate two basic conditions must be met:

core temperature must be more than 16 million K
there must be enough Carbon, Nitrogen and Oxygen present

This cycle is only significant for stars more massive than 1.1 solar masses. When in effect, the CNO is a more efficient energy generation method than the p-p cycle. Note that this reaction is a catalytic reaction. The Carbon used to "initiate" the reaction is returned at the end. It is not burning Carbon, Nitrogen or Oxygen - they are vehicles being used to convert Hydrogen into Helium.