Wet shampoo cleaning with rotary machines, followed by thorough wet vacuuming, was widespread until about the 1970s, but industry perception of shampoo cleaning changed with the advent of encapsulation. Hot-water extraction, also regarded as preferable by all manufacturers, had not been introduced either. Wet shampoos were once formulated from coconut oil soaps, wet shampoo residues can be foamy or sticky, and steam cleaning often reveals dirt unextracted by shampoos.

Since no rinse is performed, the powerful residue can continue to collect dirt after cleaning, leading to the misconception that carpet cleaning can lead to the carpet getting "dirtier faster" after the cleaning. The best method is truckmounted hot water extraction.

When wet-shampoo chemistry standards converted from coconut oil soaps to synthetic detergents as a base, the shampoos dried to a powder, and loosened dirt would attach to the powder components, requiring vacuuming by the consumer the day after cleaning.