Final answer:
Licensees may not use substances labeled "for external use only" and disinfectants in performing cosmetology services, but shampoo is safe to use. Hand sanitizers may not be suitable for certain cosmetology services.
Step-by-step explanation:
In performing cosmetology services, licensees are prohibited from using substances labeled "for external use only" as these may not be suitable for direct application on clients' skin. This is because these substances, such as certain ointments or medications, are formulated for specific purposes and may have different effects when applied topically. Licensees also need to be cautious with disinfectants, as these products are meant for cleaning and sanitizing surfaces rather than being directly applied to the skin. Shampoo, on the other hand, is commonly used in cosmetology services and is safe for use. Hand sanitizers, although useful for personal hygiene, may not be appropriate for certain cosmetology services where water and soap are recommended for handwashing.