Fish oil safety in a shellfish allergic patient

In a patient that is allergic strictly to shellfish and tolerates finned fish, it is very unlikely that the fish oil would present a risk for an allergic reaction. Additionally, fish oil supplements go through an extensive process to remove impurities. These extended processes should eliminate the protein allergen, but this cannot be guaranteed.

I was unable to find a reference specifically addressing this question, however I did find a few addressing fish oil in fish allergy patients.

Howard-Thompson, et al (1) published a case report of an adult with known fish allergy who began taking fish oil supplements. On day four experienced chest tightness, shortness of breath, tingling of upper extremities, flushing, and pruritus and was seen in the ED. Subsequently the patient stopped taking the supplement and all symptoms resolved. Based on the temporal association it was determined that the fish oil supplement was likely causal.

A small study of six patients with known fish allergy were evaluated to determine the safety of taking fish oil. They were skin tested with two different fish oil supplements and given an oral challenge of each supplement one hour apart. Vital signs were measured at baseline and at 20-minute intervals after each challenge. Spirometry was measured at baseline and one hour after each challenge. Six of six patients with positive skin tests to at least one finned fish had negative skin tests to the two fish oils, and each passed the oral challenges. (2)

Neither of these are robust enough to clearly answer the question, nor do they address shellfish allergy. There could be a very small, but potential risk, including variability from one fish oil to the next. It is not clear whether fish oil is safe for people who are allergic to seafood, though in a patient that tolerates finned fish the risk would quite low. It may be reasonable to do an in-office oral challenge.

1) Howard-Thompson A, Dutton A, Hoover R, Goodfred J. Flushing and pruritus secondary to prescription fish oil ingestion in a patient with allergy to fish. Int J Clin Pharm. 2014 Dec;36(6):1126-9. doi: 10.1007/s11096-014-0017-8. Epub 2014 Oct 16. PMID: 25314925.

2) Mark BJ, Beaty AD, Slavin RG. Are fish oil supplements safe in finned fish-allergic patients? Allergy Asthma Proc. 2008 Sep-Oct;29(5):528-9. doi: 10.2500/aap.2008.29.3159. PMID: 18926060.

Jeffrey G. Demain, MD, FAAAAI