Final answer:
If a client is allergic to seaweed, they should avoid anything containing algae.
Step-by-step explanation:
If a client is allergic to seaweed, they should avoid anything containing algae. Algae is a type of seaweed and can trigger an allergic reaction in individuals who are allergic to seaweed. While essential oils, fragrance-free products, and synthetic additives do not necessarily contain seaweed, it is always important to check the ingredient labels to ensure that they do not include any form of seaweed or algae.