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During first dredge-up, the convective envelope deepens on the red-giant branch and brings CNO cycle-processed material to the surface, increasing helium and nitrogen while reducing carbon and changing isotopic ratios. After central helium exhaustion, second dredge-up occurs in this intermediate-mass range: the envelope penetrates into layers processed by hydrogen and sometimes helium burning, lowers the hydrogen-exhausted core mass, and further enriches the surface in helium and nitrogen.

During the thermally pulsing Asymptotic giant branch, a helium-shell flash can be followed by third dredge-up. The envelope then reaches the intershell and may expose newly synthesized carbon and slow-neutron-capture products. In the more massive objects, hot-bottom burning at the base of the convective envelope can convert some dredged-up carbon into nitrogen.