Final answer:
A manufacturer may be responsible for a client's allergic reaction if they were aware of the potential allergenic nature of the product or if the product was defectively designed or manufactured.
Step-by-step explanation:
A manufacturer may be responsible for a client's allergic reaction to a product if the manufacturer is aware of the potential for the product to cause allergies or if the product is found to be defectively designed or manufactured. In such cases, the manufacturer may be held liable for any harm caused to the client. For example, if a manufacturer of a cosmetic product uses a known allergen as an ingredient without proper warning labels, and a client has an allergic reaction to the product, the manufacturer could be held responsible.