Final answer:
A cosmetologist should wash hands with warm water and soap before performing a service to maintain proper hygiene and prevent the spread of germs.
Step-by-step explanation:
Before performing a service, a cosmetologist should wash hands with warm water and soap. This is an essential step to ensure proper hygiene and prevent the spread of germs and infections. Cosmetologists should follow the recommended handwashing technique, which includes wetting hands with water, applying soap, lathering for at least 20 seconds, and rinsing thoroughly. After washing, hands should be dried with a clean towel or hot air blower and any used towels should be properly disposed of.