What is a food allergy?

A food allergy is a condition in which certain foods trigger an abnormal immune response.

It’s caused by your immune system wrongly recognizing some of the proteins in a portion of food as harmful. Your body then launches a range of protective measures, including releasing chemicals like histamine, which causes inflammation.

For people with a food allergy, even exposure to minimal amounts of the problem food can cause an allergic reaction.

Adult food allergy symptoms

Symptoms can occur anywhere from a few minutes after exposure to a few hours or even a few days later, depending on the type of allergy. They may include some of the following:

• Difficulty breathing
• Low blood pressure
• Vomiting
• Diarrhea
• Hives
• Itchy rash
• Swelling of the tongue, mouth, or face

Many food intolerances are often mistaken for food allergies. However, food intolerances never involve the immune system. While they can severely affect your quality of life, they are not life-threatening.

Here are the eight most common food allergies for adults.

Shellfish

A shellfish allergy is caused by your body attacking proteins from the crustacean and mollusk families of fish, which are known as shellfish.

Examples of shellfish include:

• Shrimp
• Prawns
• Crayfish
• Lobster
• Squid
• Scallops

The most common trigger of a seafood allergy is a protein called tropomyosin. Other proteins that may play a role in triggering an immune response are arginine kinase and parvalbumin. Symptoms of a shellfish allergy usually come on quickly and are similar to other IgE food allergies. 

However, an authentic seafood allergy can sometimes be hard to distinguish from an adverse reaction to a seafood contaminant, such as bacteria, viruses, or parasites.

The symptoms can be similar, as both can cause digestive issues like vomiting, diarrhea, and stomach pain.

A shellfish allergy doesn’t tend to resolve over time, so most people with the condition must exclude all shellfish from their diet to avoid having an allergic reaction.

Interestingly, even the vapours from cooking shellfish can trigger a shellfish allergy in those who are allergic. This means that many people are also advised to avoid being around seafood when it’s being cooked.

Peanuts

Like a tree nut allergy, peanut allergies are very common and can cause severe and potentially fatal allergic reactions.

However, the two conditions are considered distinct, as a peanut is a legume. Nevertheless, those with peanut allergies are often also allergic to tree nuts.

While the reason people develop a peanut allergy isn’t known, it is thought that people with a family history of peanut allergies are most at risk.

Because of this, it was previously thought that introducing peanuts through a breastfeeding mother’s diet or during weaning may trigger a peanut allergy.

However, studies have since shown that introducing peanuts early may be protective.

Peanut allergies affect around 1–3% of children and up to 2% of adults.

However, around 15–22% of children who develop a peanut allergy will find it resolves as they move into their teenage years.

Like other allergies, a peanut allergy is diagnosed using a combination of:

• Health history
• Skin-prick testing
• Blood tests
• Food challenges

At the moment, the only effective treatment is avoidance of all peanuts and peanut-containing products.

However, new treatments are being developed for children with peanut allergies. These involve giving precise and small amounts of peanuts or peanut allergen powder under strict medical supervision in an attempt to desensitize them to the allergy.

Eggs

An egg allergy is the second most common cause of food allergy in children.

However, 68% of children who are allergic to eggs will outgrow their allergy by the time they’re 16 years old.

Symptoms include:

• Digestive distress, such as a stomach ache
• Skin reactions, such as hives or a rash 
• Respiratory problems
• Anaphylaxis (which is rare)

It’s possible to be allergic to egg whites but not the yolks, and vice versa. This is because the proteins in egg whites and egg yolks differ slightly.

Yet, most proteins that trigger an allergy are found in egg whites, so an egg white allergy is more common.

Like other allergies, the treatment for an egg allergy is an egg-free diet.

However, you may not have to avoid all egg-related foods, as heating eggs can change the shape of the allergy-causing proteins. This can stop your body from seeing them as harmful, meaning they’re less likely to cause a reaction.

In fact, one study found that nearly 67% of children with an egg allergy could tolerate eating muffins containing a cooked egg component.

Some studies have also shown that introducing baked goods to children with an egg allergy can shorten the time it takes for them to outgrow the condition; however, results are conflicting, and more data is needed to confirm this.

The consequences of ingesting eggs when you are allergic to them can be severe. Because of this, you should check with your doctor before you reintroduce any egg-containing foods.

Wheat

A wheat allergy is an allergic response to one of the proteins found in wheat.

It tends to affect children the most. Although, children with a wheat allergy often outgrow it by the time they reach 10 years old.

Like other allergies, a wheat allergy can result in digestive distress, hives, vomiting, rashes, swelling, and in severe cases, anaphylaxis.

It’s often confused with celiac disease and non-celiac gluten sensitivity, which can have similar digestive symptoms.

However, a true wheat allergy causes an immune response to one of the hundreds of proteins found in wheat. This reaction can be severe and sometimes even fatal.

Celiac disease and non-celiac gluten sensitivity are caused by an abnormal immune reaction to one specific protein — gluten — that also happens to be found in wheat.

Celiac disease can also be fatal in 10 to 30% of people, though this is rare as most are able to avoid gluten (40) successfully.

People with celiac disease or non-celiac gluten sensitivity have to avoid wheat and other grains that contain the protein gluten.

Those with a wheat allergy only need to avoid wheat and can tolerate gluten from grains that do not contain wheat.

A wheat allergy is often diagnosed through skin-prick testing.

The only treatment is to avoid wheat and wheat-containing products. This means avoiding foods, as well as beauty and cosmetic products, that contain wheat.

Fish

Fish allergies are common, affecting up to around 7% of adults.

Similar to other allergies, people often develop fish allergies during childhood. But it’s not uncommon for a fish allergy to surface later in life.

Like a shellfish allergy, a fish allergy can cause a serious and potentially fatal allergic reaction. The main symptoms are vomiting and diarrhoea, but in rare cases, anaphylaxis can also occur.

This means that those who are allergic to fish are usually given an epinephrine auto-injector to carry in case they accidentally eat fish.

Because the symptoms can be similar, a fish allergy is sometimes confused for a reaction to a contaminant in fish, such as bacteria, viruses, or toxins.

Moreover, since shellfish and fish with fins don’t carry the same proteins, people who are allergic to shellfish may not be allergic to fish.

However, many people with a fish allergy are allergic to one or more types of fish.