Final answer:
The chemical straightening procedure that needs a base cream is Relaxing, to protect the scalp from harsh chemicals.
Step-by-step explanation:
The chemical straightening procedure that requires a base cream is Relaxing. This procedure involves applying a chemical relaxer to the hair, which breaks down the bonds that give hair its natural curl or wave. To protect the scalp and hairline from the potentially harsh chemicals in the relaxer, a base cream is applied before the treatment begins. This cream creates a protective barrier to prevent burns and irritation. The process is different from perming, which uses chemicals to add curls or waves to the hair, and from smoothing and keratin treatments, which typically do not require a base cream.