What is an allergy?

Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.

Common allergens include pollen and certain food. Metals and other substances may also cause problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine. Diagnosis is typically based on a person’s medical history. Further testing of the skin or blood may be useful in certain cases. Positive tests, however, may not mean there is a significant allergy to the substance in question.

Early exposure to potential allergens may be protective. Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines. In severe reactions injectable adrenaline (epinephrine) is recommended. Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear.

Symptoms

An allergic reaction causes inflammation and irritation. The signs and symptoms depend on the type of allergen. Allergic reactions may occur in the gut, skin, sinuses, airways, eyes, and nasal passages.

Allergic reactions may be confused for other conditions. Hay fever, for example, creates similar irritations to the common cold but the causes are different.

Below is a range of various triggers and the symptoms they regularly cause in people who are allergic.

Dust and pollen

blocked nose
itchy eyes and nose
runny nose
swollen and watery eyes
cough

Skin reactions

flaking
itching
peeling
rashes

Food

vomiting
swollen tongue
tingling in the mouth
swelling of the lips, face, and throat
stomach cramps
shortness of breath
rectal bleeding, mainly in children
itchiness in the mouth
diarrhea

Insect stings

wheezing
swelling at the site of the sting
a sudden drop in blood pressure
itchy skin
shortness of breath
restlessness
hives, a red and very itchy rash that spreads across the body
dizziness
cough
chest tightness
anxiety
possible anaphylaxis

Medication:

wheezing
swollen tongue, lips, and face
skin rash
itchiness
possible anaphylaxis

Anaphylaxis

Anaphylaxis is a quickly escalating, serious allergic reaction that sets in rapidly. It can be life-threatening and must be treated as a medical emergency.

This type of allergic reaction presents several different symptoms that can appear minutes or hours after exposure to the allergen. If the exposure is intravenous, onset is usually between 5 to 30 minutes. A food allergen will take longer to trigger anaphylactic reaction.

Researchers reported in The Journal of Allergy & Clinical Immunology that the most commonly affected areas in anaphylaxis are the skin and respiratory system.

Symptoms of anaphylaxis include:

hives all over the body, flushing, and itchiness
swollen tissues
a burning sensation
swelling of the tongue and throat.
a possible blue tint to the skin from lack of oxygen
a runny nose
shortness of breath and wheezing
hoarseness
pain when swallowing
cough
a drop in blood pressure that can speed up or slow down the heart rate
abdominal cramps
diarrhea
vomiting
loss of bladder control
pelvic pain similar to uterine cramps
coronary artery spasm
low blood pressure leading to high or low heart rate
dizziness and fainting

Recognizing these symptoms can be crucial to receiving timely treatment.

Causes

A particular antibody called immunoglobin (IgE) causes allergic reactions. Antibodies are released to combat foreign and potentially harmful substances in the body.

IgE is released to destroy the allergen and causes the production of chemicals that trigger the allergic reaction.

One of these chemicals is called histamine. Histamine causes tightening of the muscles in the airways and the walls of blood vessels. It also instructs the lining of the nose to produce more mucus.

Risk factors

The following can be risk factors for developing allergies:

a family history of asthma or allergies
being a child
having asthma
not being exposed to enough sunlight
having a different allergy
birth by Caesarean section

The most common allergens

Potential allergens can appear almost anywhere.

Any food can theoretically cause an allergy. Specific components of food can also trigger allergic reactions, such as gluten, the protein found in wheat. The eight foods most likely to cause allergies are:

eggs, especially egg-white
fish
milk
nuts from trees
peanuts
wheat
soy
shellfish

Other allergens include:

animal materials, such as dust mite excrement, wool, fur, dander, or skin flakes, as well as Fel d 1, a protein found in cat saliva
medications, such as penicillin, salicylates, and sulfonamides
foods such as corn, celery, pumpkin, sesame, and beans
insect stings, including wasp and bee sting venom, mosquito stings, and fire ants.
insect bites from horseflies, blackflies, fleas, and kissing bugs
cockroaches, caddis and lake flies, midges, and moths
plant pollens from grass, trees, and weeds
household chemicals
metals, such as nickel, cobalt, chromium, and zinc
latex

Diagnosis

The doctor will ask the patient questions regarding symptoms, when they occur, how often, and what seems to cause them. They will also ask the person with symptoms whether there is a family history of allergies, and if other household members have allergies.

The doctor will either recommend some tests to find out which allergen is causing symptoms or refer the patient to a specialist.

Below are some examples of allergy tests:

Blood test: This measures the level of IgE antibodies released by the immune system. This test is sometimes called the radioallergosorbent test (RAST)
Skin prick test: This is also known as puncture testing or prick testing. The skin is pricked with a small amount of a possible allergen. If the skin reacts and becomes itchy, red, and swollen, it may mean an allergy is present.
Patch test: A patch test can identify eczema. Special metal discs with very small amounts of a suspected allergen are taped onto the individual’s back. The doctor checks for a skin reaction 48 hours later, and then again after a couple of days.

The American College of Allergy, Asthma and Immunology can help you find a certified allergist.

Even if the patient knows what triggers the allergy, the doctor will carry out tests to determine which particular substance is causing symptoms.

Preventing symptoms

There’s no way to prevent allergies. But there are ways to prevent the symptoms from occurring. The best way to prevent allergy symptoms is to avoid the allergens that trigger them.

Avoidance is the most effective way to prevent food allergy symptoms. An elimination diet can help you determine the cause of your allergies so you know how to avoid them. To help you avoid food allergens, thoroughly read food labels and ask questions while dining out.

Preventing seasonal, contact, and other allergies comes down to knowing where the allergens are located and how to avoid them. If you’re allergic to dust, for example, you can help reduce symptoms by installing proper air filters in your home, getting your air ducts professionally cleaned, and dusting your home regularly.

Proper allergy testing can help you pinpoint your exact triggers, which makes them easier to avoid. These other tips can also help you avoid dangerous allergic reactions.

Complications of allergies

While you may think of allergies as those pesky sniffles and sneezes that come around every new season, some of these allergic reactions can actually be life-threatening.

Anaphylaxis, for example, is a serious reaction to the exposure of allergens. Most people associate anaphylaxis with food, but any allergen can cause the telltale signs:

suddenly narrowed airways
increased heart rate
possible swelling of the tongue and mouth

Allergy symptoms can create many complications. Your doctor can help determine the cause of your symptoms as well as the difference between a sensitivity and a full-blown allergy. Your doctor can also teach you how to manage your allergy symptoms so that you can avoid the worst complications.

Treatment

The most effective treatment and management of an allergy is avoidance of the allergen.

However, sometimes it is not possible to completely avoid an allergen. Pollen, for example, is constantly floating in the air, especially during hay fever season.

Medications

Drugs can help treat the symptoms of an allergic reaction, but they will not cure the allergy. The majority of allergy medications are over-the-counter (OTC). Before taking a particular type of medication, speak to a pharmacist or doctor.

Antihistamines: These block the action of histamine. Caution is recommended, as some antihistamines are not suitable for children.
Decongestants: These can help with a blocked nose in cases of hay fever, pet allergy, or dust allergy. Decongestants are short-term medications.
Leukotriene receptor antagonists, or anti-leukotrienes: When other asthma treatments have not worked, anti-leukotrienes can block the effects of leukotrienes. These are the chemicals that cause swelling. The body releases leukotrienes during an allergic reaction.
Steroid sprays: Applied to the inside lining of the nose, corticosteroid sprays help reduce nasal congestion.

Immunotherapy

Immunotherapy is also known as hyposensitization. This type of therapy rehabilitates the immune system. The doctor administers gradually increasing doses of allergens over a period of years.

The aim is to induce long-term tolerance by reducing the tendency of the allergen to trigger IgE production.

Immunotherapy is only used to treat severe allergies.

Treatment for anaphylaxis

Anaphylaxis is a medical emergency. The patient may require resuscitation, including airway management, supplemental oxygen, intravenous fluids, and close monitoring.

The person experiencing anaphylaxis will need an injection of adrenaline into the muscle. Antihistamines and steroids are often used alongside the adrenaline injection.

After the patient has been stabilized, doctors may recommend remaining in hospital under observation for up to 24 hours to rule out biphasic anaphylaxis. Biphasic anaphylaxis is the recurrence of anaphylaxis within 72 hours with no further exposure to the allergen.

Patients who have had severe allergic reactions should carry an epinephrine autoinjector with them, such as the EpiPen, EpiPen Jr, Twinject, or Anapen.

Many doctors and health authorities advise patients to wear a medical information bracelet or necklace with information about their condition.

How to prevent allergies

There is no way to prevent an allergy. However, it is possible to limit symptoms.

Even though treatments can help alleviate allergy symptoms, patients will need to try to avoid exposure to specific allergens. In some cases, this is not easy. Avoiding pollen in late spring and summer is virtually impossible, and even the cleanest houses have fungal spores or dust mites.

If you have friends or family with pets, avoiding them might be difficult. Food allergies can be challenging to manage because traces of allergens can appear in unlikely meals. However, being vigilant about checking food packages can be a key way to avoid consuming certain allergens.

Make sure you receive proper allergy testing and know what substances to avoid.

Natural remedies for allergies

Many natural remedies and supplements are marketed as a treatment and even a way to prevent allergies. Discuss these with your doctor before trying them. Some natural treatments may actually contain other allergens and make your symptoms worse.

For example, some dried teas use flowers and plants that are closely related to plants that might be causing you serious sneezing. The same is true for essential oils. Some people use these oils to relieve common symptoms of allergies, but essential oils still contain ingredients that can cause allergies.

Each type of allergy has a host of natural remedies that may help speed up recovery. There are also natural options for children’s allergies, too.

Frequently Asked Questions

What is the difference between food allergy and food intolerance?
A food allergy occurs when the immune system reacts to a certain food. The symptoms typically include hives, swelling of the throat or tongue, nausea, and loss of consciousness.

A food intolerance is caused by an enzyme deficiency; it does not involve the immune system. Lactose intolerance is an example. A person with lactose intolerance lacks an enzyme that is needed to digest milk sugar. When the person eats milk products, symptoms such as gas, bloating, and abdominal pain may occur.

If I change my diet while I am pregnant, will this prevent my child from having food allergies?

Excluding common allergy causing foods (such as peanut, egg, fish, soy, and cow’s milk), from a pregnant mother’s diet has not been shown to reduce the chance of children having food allergies. It has however been linked with low weight gain by babies. Restricted diets during pregnancy are therefore not recommended.

If I change my diet while I breastfeed my baby, will this prevent my child from having food allergies?

Studies have not shown that excluding common allergy causing foods from a breastfeeding mother’s diet reduces the chance of a child having food allergies. Restricted diets are therefore not recommended.

Are there any foods I should not feed my child when starting solid foods?

You should start feeding solid foods to your baby around six months of age (not before four months), and when your baby is ready, preferably whilst you still breastfeed your baby. Common allergy causing foods should be fed to your baby before 12 months of age. Studies of babies at high risk of having allergies have shown that this reduces the chance of them developing food allergies.

Why should solid foods not be started before four months?

Studies have shown that babies at high risk of having allergies who are exclusively breastfed for the first three to four months of life are less likely to develop food allergies and eczema during the first two years of life. There are also developmental reasons why solid foods should not be started before four months, as a baby’s digestive system and ability to chew and swallow are not yet fully developed or ready for solid foods..

What should I do if my child has a food allergy?

If you suspect that your child has a food allergy, ask your doctor for advice before introducing that food.

In children with confirmed cow’s milk and soy allergy, special formula can be prescribed by a doctor.

Food restrictions should be discussed and supervised by your doctor, who may also recommend a dietitian.

Is soy milk or goat’s milk better to prevent allergies in my child than cow’s milk formula?

No. Studies have shown that the use of soy milk or goats milk formula does not prevent development of food allergies in children.

Should I avoid pets?

There is no reason to remove pets from the household unless a person is already allergic to them and has symptoms when exposed to the pet.

Will dust mite avoidance measures reduce the risk of allergy and asthma developing?

Unless a person is already allergic to dust mites, there is no convincing evidence at this time that dust mite avoidance or minimisation measures reduce the risk of developing allergy or asthma,

Will taking fish oils prevent allergy?

There is no convincing evidence at this time, which has shown that taking fish oil supplements during pregnancy has any significant benefit in preventing allergy.

Are probiotics useful in preventing allergies?

Probiotics are not currently recommended for preventing allergies. There are conflicting studies on the benefit of giving probiotics for the prevention of allergic disease. Whilst some studies have found a protective effect against the development of eczema, other studies have shown no effect on the development of allergic diseases. Further studies are required to confirm the role of probiotics in the prevention of allergic disease.

Will allergen immunotherapy (desensitisation) prevent allergy?

The current role of allergen immunotherapy is to treat established environmental allergies. However, there is some emerging evidence that treating children who have allergic rhinitis (hay fever) with allergen immunotherapy to “switch off” allergy may reduce the risk of them developing asthma, or further aeroallergen sensitivities later in life. This is an area of active research.

Allergies