Here is our guide
and advice on the problem. It is of course not comprehensive as there are always
other things which may creating allergies.
Adverse reactions to shellfish are rare in young children, and are
usually not seen until the teenage years or adulthood. This may be a
reflection of the fact that shellfish is not normally a part of the diet
of young children.
Allergy to fish - such as cod and other white fish - may begin in
childhood and is likely to be lifelong.
Allergies to shellfish or fish
are potentially serious and there may be a rapid onset of symptoms. A
GP's or MD's advice should be sought in all cases and a referral made to see an
allergy specialist. Patients known to be at risk may be prescribed
auto-injectors containing adrenaline (also known as epinephrine).
Someone who reacts to one type of fish - even if the symptoms are mild -
might be advised to play safe and eliminate all fish from their diet.
This is partly because they may react to another type of fish, but also
because of the high risk of cross-contamination among different types of
fish (e.g. at fish markets or on fish counters).
This also applies to shellfish. People allergic to one type of shellfish
are often advised to avoid all shellfish.
Different types of shellfish
Biologically speaking, shellfish are aquatic invertebrates rather than
fish. They can be divided into two main groups:
(e.g. crab, lobster, crayfish, shrimp, prawn)
(a) Bivalves (e.g. mussels, oysters, scallops, clams)
(b) Gastropods (e.g. limpets, periwinkles, snails)
(c) Cephalopods (e.g. squid, cuttlefish, octopus)
People who have reacted to one type of shellfish (e.g. crab) are likely
to react to other members of the same group (in this case, other
crustaceans). If you react to crab, avoid that and the rest of the
crustacean group. If you react to squid, avoid that and the rest of the
cephalopod group. Shellfish from the other groups may not necessarily
present a problem, although they may do for some people. It is advisable
to avoid them anyway. A special reason for being cautious is that there
is a relatively high risk of cross-contamination among different types
Kosher food is shellfish-free. Always read the labels and check with
food companies if you are unsure.
Should people with shellfish allergy
avoid fish, and vice versa?
Fish and shellfish are biologically distinct. People who are
shellfish-allergic may be able to eat fish, and vice versa - unless they
have both allergies. But as stated above, be aware of the risk of cross
contamination in restaurants, markets and open fish counters. If the
same pair of tongs is used to handle different types of fish and
shellfish, or if you suspect one type of fish or shellfish may have
spilled over and had contact with another, you should avoid buying or
People have been known to go into anaphylactic shock after breathing in
airborne particles of shellfish or fish allergen in open fish markets.
Avoiding shellfish and fish in restaurants
In restaurants, inform staff of your allergy. Find out what your food is
fried in, and whether the oil has been used for anything else. Check the
ingredients of all stocks and soups. Ideally, your companions should
avoid eating fish/shellfish in your presence, as there is a small risk
that breathing in the cooked food may cause a reaction.
As they are relatively expensive, shellfish and fish are rarely an
undeclared or unexpected ingredient in pre-packaged foods. Always check
the label for the type of shellfish/fish to which you are allergic. Some
supermarkets (e.g. Publix, Sainsbury's) will have a "CONTAINS" bar, which will
indicate the presence of fish and shellfish, but policies vary from
store to store and brand to brand. Be vigilant when choosing stocks,
soups and highly processed foods, which may contain shellfish or fish
extract to add flavour.
Shellfish and fish allergy: dishes to look out for
Dishes to look out for include paella, bouillabaisse, gumbo (a Tex Mex
dish), frito misto (a mixed fried fish dish from the Mediterranean
coast), and fruits de mer (seafood). Oriental food tends to contain lots
of different kinds of fish at once, and chopped pieces can be difficult
Surimi (a processed seafood product) is usually made from white fish but
may contain shellfish extract. Surimi can be present in processed foods
such as pizza toppings.
Caesar salad dressing normally contains anchovies. Worcestershire sauce
Caponata, a traditional sweet and sour
Sicilian relish, can contain anchovies.
Kedgeree is made with rice and fish.
Fish sauce is a common ingredient in the Far East. Terms to look out for
are Nuoc Mam and Nam Pla.
Fish sauce can be made with shellfish as well as fish.
Patum Peperium (Gentleman's Relish) is a spread made with anchovies.
Check the ingredient lists on ready-made Oriental sauces, pastes and
prepared meals. In fact check the ingredient lists of all food for
The above list is not exhaustive. If you are not sure of any product,
question catering staff or shop staff.
People with shellfish allergy are sometimes warned against iodine, an
element present in a wide range of items including shellfish, seaweed,
cleaning products, and X-ray dyes. However, iodine allergy is unrelated
to shellfish allergy. The allergen present in shellfish is not iodine
but muscle protein in the flesh.
Shellfish shell and skeleton derivatives
Although it is the flesh of shellfish that contains the allergen, people
with shellfish allergy are advised to avoid shellfish shells and
1. Glucosamine, used in the treatment of arthritis, is derived
from the skeletons of shellfish and is unsuitable for people with
2. Chondroitin is a shellfish-free alternative.
derived from shellfish shells, is used in commercial "fat absorbers"
such as Chitosan HD, and should be avoided.
4. Moisturisers can also
contain shellfish-derived chitin.
5. Some calcium supplements may contain
ground oyster shells.
The cod worm
Some people who think they are reacting to seafood are actually having
an allergic reaction to a worm-like parasite called Anisakis (also known
as the cod worm). This parasite, relatively common in Spain, can cause
urticaria, gastrointestinal upset or even anaphylaxis when present in
fresh cephalopods, or hake, anchovy or cod. If you react to a particular
fish on one occasion, but subsequently eat it with no problem, you
should consider the possibility that the cod worm was responsible. Speak
to your doctor.
On rare occasions, people who think they react to seafood (or other food
for that matter) may be reacting to the latex gloves used in
preparation. They should consider the possibility that they may be latex
allergic and speak to their doctor.
Adverse reactions to seafood are not always symptomatic of genuine
sometimes present in spoiled fish (especially tuna and mackerel),
can cause a condition not unlike allergy called scrombroid
poisoning. Unlike an allergy, this would affect everyone who
consumed the offending food.
Shellfish sometimes absorb poison from toxic algal blooms (red
appear in the waters at certain times of year. This can cause
illnesses known as amnesic, diarrhetic, paralytic and neurotoxic
shellfish poisonings. These toxins will affect everyone who eats the
ALWAYS CONSULT YOUR DOCTOR OR PHARMACIST FOR FURTHER
I hope this information was of help?
Captain Tony Allen is a pharmacist by profession
and is a registered member of
THE ROYAL PHARMACEUTICAL SOCIETY OF GREAT BRITAIN #62419