Generally speaking, those who have shellfish allergies should avoid spirulina as it is a type of cyanobacteria and may contain traces of seafood proteins. Additionally, pregnant and nursing women should also avoid taking spirulina supplements due to a lack of evidence regarding its safety for use during these times. Lastly, people with autoimmune diseases such as multiple sclerosis or rheumatoid arthritis should talk to their doctor before taking any kind of dietary supplement because some research suggests that certain components in spirulina could worsen the symptoms associated with these conditions.