What type of service should be avoided if a client has a known allergy?

When considering which type of service should be avoided if a client has a known allergy, the focus is on the products and substances that could potentially trigger an allergic reaction. Services involving allergic substances or products directly relate to the use of materials or chemicals that the client is known to be allergic to. Therefore, any service that requires the application of these allergens, such as hair dye, certain shampoos, or styling products containing allergens, should be avoided to prevent adverse reactions.

Hair washing and hair cutting are typically not associated with allergens unless specific products that the client is allergic to are used. Similarly, while styling products may contain allergens, not all styling products pose a risk, and it would depend on the specific ingredients involved. Thus, the safest course of action is to avoid any service that involves known allergens to ensure the client's safety and comfort.