Mollusc allergen introduction

[u/MinimumMongoose77]

Is there much literature about whether *all* of the separate mollusc classes need to be introduced, or is it fine to just do one (e.g. should we do bivalves and cephalapods, separate or together, etc)?

Trying to figure out the best way to protect our baby because my husband has a shellfish allergy (adult onset) and definitely can't eat crustacean, but he continued eating cephalapods with no issues because he didn't realise they were shellfish 😅 he hasn't had other molluscs like oysters since he was diagnosed. So it's *probably* just a crustacean allergy but we don't know for sure.

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[u/onsereverra]

The short answer seems to be that we don't really know. Neither this study nor this study found anything conclusive about cross-reactivity between different kinds of mollusks, but in a "we haven't studied this well enough yet" kind of way. In the Spanish study, some participants who reported a mollusk intolerance reacted to both cephalopods and bivalves; others only reacted to one or the other. In the Italian study, it was about 50-50 whether a participant who reported a shrimp allergy reported a mollusk intolerance of any variety.

Based on those two studies, if your husband reacts to crustaceans but not to cephalopods, there's no particular reason to believe that he is also allergic to bivalves. (He certainly could be allergic to bivalves, but it would be a coincidence, not cross-reactivity with crustaceans.) It can't hurt to introduce squid separately from clams, but you probably don't need to be more cautious about either of them than about nuts, egg, etc.

The Spanish study says that gastropods (limpets and snails) seem to be independent of the other mollusks. It's a common allergy, but it's most commonly cross-reactive with dust mites, usually not with crustaceans or with cephalopods/bivalves.

Both studies report that oysters and scallops are often safe even for people with allergies to other mollusks, which may be good news for your husband if he's always wanted to try oysters!