Crustaceans

Crustaceans are shellfish with a hard, jointed outer shell. The group includes shrimp (prawns in the UK), crab, lobster, crayfish (crawfish), langoustine and krill. A crustacean allergy is one of the most common seafood allergies in adults, and cooking does not destroy the proteins that cause it. A doctor can confirm the allergy and tell you what to avoid.

How to use it

Both the EU and the US treat crustaceans as a major allergen:

• In the EU and the UK, crustaceans are one of the 14 allergens and must be emphasized in the ingredients list.
• In the US, crustacean shellfish are one of the nine major allergens, and the label must name the species, such as "shrimp" or "crab".

The rules differ for mollusks such as mussels, squid and oysters. The EU lists them as a separate allergen, but the US does not count them as a major allergen. Some people who react to crustaceans also react to mollusks. Ask an allergist which you need to avoid.

Common mistakes

• Picking shrimp out of a dish. The proteins stay in the sauce.
• Sharing frying oil. Fried food can pick up shellfish protein from oil used for shrimp tempura or breaded scampi.
• Ignoring cooking steam. Some people react to the vapor from boiling or steaming shellfish.
• Assuming a dish without visible seafood is safe. Pastes and sauces can contain dried shrimp.

In recipes

Look for crustaceans in these less obvious places:

• Shrimp paste, which is used in many Thai, Malaysian and Indonesian curry pastes and sambals
• Dried shrimp in Chinese and Southeast Asian cooking, and in some XO sauce
• Some fish sauce brands, which add shrimp; fish sauce is usually made from anchovies
• Seafood stocks, bisque, gumbo and paella
• Imitation crab (surimi), which may contain crab extract

If you have a crustacean allergy, read labels every time, ask in restaurants how dishes are made, and talk to a doctor about a plan for accidental exposure.