What type of service requires professional guidance before performing on clients?

Chemical straightening services require professional guidance before performing on clients because they involve the use of strong chemicals that can significantly alter the structure of the hair. These products are designed to break down the hair's natural bonds, allowing it to be reshaped, which can lead to damage if not applied correctly. Proper training ensures that the barber or stylist can assess the client's hair type, scalp condition, and desired results, minimizing the risk of adverse reactions or hair damage.

Although hair coloring services also involve chemicals, many professionals are equipped to handle these with proper training and do not always necessitate as extensive a level of expertise as chemical straightening. Haircuts and shaving are more straightforward services that, while requiring skill, generally do not involve chemical processes that could jeopardize the health of the hair or scalp.