Some shellfish reactions are not true allergies but are caused by marine toxins from contaminated shellfish.
| Feature | Shellfish Allergy | Shellfish Poisoning (Toxic Reaction) |
| Cause | IgE immune reaction to shellfish proteins | Toxins from algae-contaminated shellfish |
| Symptoms | Hives, anaphylaxis, swelling | Nausea, vomiting, neurological issues |
| Onset | Minutes to hours | 30 minutes to 24 hours |
| Triggers | Any shellfish species (allergy-dependent) | Bivalves (clams, mussels, oysters, scallops) |
| Treatment | Epinephrine, antihistamines, strict avoidance | Medical support, no specific antidote |
Shellfish poisoning can mimic an allergic reaction but is caused by toxins rather than an immune response.