An allergy is defined as an inappropriate and harmful response of the body’s immune system to substances that are in normal instances harmless.
Table of Contents [Show]
- Allergy Types
- Allergy Symptoms
- Allergy causes
- Risk Factors
- Diagnosis and Treatments
The body’s immune system mediates an allergic reaction, and the process is mostly controlled by an antibody called immunoglobulin E (IgE).
Researchers do not know why people develop allergies, but there are many proposed hypotheses with the “hygiene hypothesis” being the most controversial one.
Current research on allergies is advanced and has discovered all the intricate details behind the molecular and cellular mechanisms behind allergies.
For this reason, successful treatment for allergies is now made possible.
But despite, this, the factors that contribute to the development of allergies are still poorly understood explains Baroness Ilora Finlay in her foreword for the WAO White Book on Allergy: 2013 Update.
This is rather concerning because we’re currently witnessing a worldwide allergy epidemic affecting more than 20% of people in developed countries.
It’s interesting to note that the prevalence of allergies varies between 1% and 40% between countries and affluence and lifestyle seem to play a big part in this discrepancy.
There are many types of allergies divided according to the type of allergen (substance triggering the allergy) and location of the allergic reaction.
Allergies also vary in their severity from being relatively mild to life-threatening.
Allergy is diagnosed by a doctor called an “allergist” who looks at a patient’s symptoms and performs allergy testing to determine the type of allergy.
Once a doctor has determined the type of allergy, they will suggest treatment options.
Treatment includes avoiding the substance causing the allergic reaction, taking allergy medication, and allergy shots.
Although these treatments are successful in controlling the allergy, they usually don’t cure the allergy.
Allergy in adults is usually considered a chronic disease.
Children, on the other hand, may outgrow an allergy despite being the population group with the highest allergy prevalence.
Because a significant portion of the world’s population suffers from some allergy, allergy education has become more critical than ever.
The largest allergy organization in the world, called The World Allergy Organization (WAO), understands the importance allergy research plays in controlling this growing epidemic and as such, aims to educate medical professionals and the broader public on current findings in the allergy research fields.
In the next chapters, we will cover the facts about allergy taken from WAO’s literature and other related research findings.
The topics covered include types of allergies, common allergy symptoms, causes of allergies, risk factors, and treatment options.
There seem to be as many types of allergies as there are organs in the human body and as there are environmental substances.
As a result, researchers have developed many different sub-divisions of allergies.
But to simplify things, allergies are divided here into the manner of allergen intake and into the four classifications that denote allergy severity and cause.
In this article, we cover the most common types of allergies.
- Inhalation allergies happen when a person breathes in an allergen such as pollen, dust, fungus spores, animal hairs, etc. The allergy usually manifests as a runny nose, itchy eyes, sore throat, and wheezing. These allergies are usually a reaction to the protein molecule found in the allergen.
- Food allergies happen when someone eats a food that contains an allergen. Most common food allergies are nut, seafood, fruit, wheat, cow’s milk, eggs, and rice allergies. These need to be distinguished from food intolerances which have different causes and symptoms.
- Medication allergies happen when someone takes a type of medicine containing the common allergen. Aspirin and penicillin are two of the most common types of medicine that some people are allergic to.
- Insect bite allergies happen with insect bites and stings. Most allergic reactions happen due to the venom being injected into their skin and bloodstream from insects like bees, wasps, hornets, and mosquitos. Most people show some allergic reaction to insect bites, but a reaction is considered allergic when it is more severe than would be considered normal.
- Contact allergies happen through skin contact with an allergen such as certain metals or cosmetics. The reaction can remain localized on the skin or lead to a whole-body allergic reaction (anaphylaxis).
Allergy Classification According To Reaction
Allergy classification, according to reaction type, is explained below.
While most allergic reactions are mediated by IgE, the systems that lead to the different types of reactions involve a whole cascade of events that researchers divided into the following types:
- Type I allergies, also called immediate allergies are the most common types of allergies. Examples include hay fever, asthma, food allergies, and insect allergies. These allergies are usually a result of our bodies reacting to the protein molecules in the allergen by increasing the amount of IgE in the body.
- Type II allergies, known as cytotoxic hypersensitivity allergies, are less common and lead to a severe reaction that can damage blood cells. They are called cytotoxic because they lead to an immune response that leads to cell death. The usual cause of these types of allergies is medication.
- Type III allergies are also called immune-complex reactions, and they are more common than type II allergies. These allergies are characterized by tissue damage that happens as a result of the formation of an immune antigen-antibody complex that starts accumulating in different bodily tissue causing damage. The tissue usually affected includes the kidneys, blood vessels, the joints, and the skin.
- Type IV allergies are known as delayed-hypersensitivity and involve the T-cell (types of defense cells) response to an allergen. They are called delayed-hypersensitivity because the first symptoms tend to appear between 24 hours and three days upon exposure to an allergen. Allergens that usually cause Type IV allergies are small molecules from metals and chemicals and they usually manifest as eczema.
Allergies can also be divided into seasonal allergies and occupational allergies.
Seasonal allergies are what we usually refer to as hay fever and involve allergy to a specific or any plant pollen.
Occupational allergies happen when a person develops an allergy to substances that they’re exposed to at work.
Examples of occupational allergies include people working with paint, plastics, and foam and hairdressers chronically exposed to perm agents.
But in general, most experts tend to focus on the substance causing the allergic reaction, and in such cases, a person is said to be suffering from, say, a peanut allergy, pollen allergy, penicillin allergy, or metal allergy.
The allergic reaction can be mild as in the case of hay fever or severe as in the case of anaphylaxis.
Anaphylaxis is a medical emergency as this type of allergic reaction often leads to shock in addition to a skin rash, facial swelling, nausea, vomiting, diarrhea, and airway obstruction.
Anaphylaxis is a Type I allergic reaction, and it occurs between 15 and 30 minutes upon exposure to an allergen. Allergies that could trigger anaphylaxis include food, medication, and insect bite allergies.
Allergies can lead to a range of symptoms that can be either mild or severe, and localized or whole-body.
What symptoms a person experience helps doctors determine the type of allergy involved.
For instance, sneezing can indicate a pollen or dust allergy, while hives may be a sign of food allergies.
Allergy symptoms usually appear within minutes of being exposed to an allergen.
Rarely will a symptom occur within days of exposure to certain substances.
If you experience a sudden onset of symptoms like sneezing, a runny nose, itchiness, red and watery eyes, wheezing, facial swelling, and red skin, the chances are that this is an allergic reaction.
Pollen Allergy (Hay Fever)
Pollen allergy is the most common types of allergy, affecting up to 22.1% of children globally according to World Allergy Week.
The immune system mistakes harmless pollen for dangerous substances and starts releasing chemicals to attack the pollen, which leads to a range of symptoms such as:
- Nasal congestion
- Sinus pressure
- Runny nose
- Itchy and watery eyes
- Throat soreness
- Dark circles under the eyes
- Decreased sense of smell and taste
Food allergies can cause mild symptoms upon first ingestion of a food allergen and a severe reaction next time.
So, avoiding the food a person is allergic to is essential to prevent adverse events.
It’s hard to self-diagnose a food allergy because the symptoms of food allergies can be varied and not restricted to the gastrointestinal tract.
Some common symptoms of food allergies include:
- Stomach upset (vomiting, pain, and diarrhea)
- Hives (raised, red bumps on the skin)
- Trouble breathing
- Wheezing and coughing
- Weak pulse and skin pallor
Most of these symptoms occur within a couple of minutes or a few hours after eating a certain food.
In rare cases, will a reaction occur up to six hours upon ingesting certain foods?
Those experiencing any of the above-mentioned symptoms after having a meal need to seek medical help immediately.
Food allergies between adults and children seem to differ significantly with children experiencing allergies to eggs, peanuts, and milk and adults being more likely to suffer allergies to fruits, tree nuts, and seafood.
Medication / Drug Allergy
Drug allergy symptoms are similar to both pollen and food allergy symptoms.
They occur within an hour upon taking a particular medicine, which is usually the time it takes for a medication to enter the bloodstream.
Common symptoms of medication allergy are:
- Skin changes (rash, hives, itchiness)
- Sudden fever
- Swelling (facial, arms or legs)
- Trouble breathing
- Runny nose
- Itchy and watery eyes
Drug allergies are increasing with now 1 in 10 people believed to be suffering from at least some drug allergy.
According to the latest reports on allergy prevalence published in the journal Allergy, penicillin accounts for most of the drug allergies (12.8%), followed by sulfonamide antibiotics (7.4%), certain opiates (6.8%), and lastly by nonsteroidal anti-inflammatory drugs (NSAIDs) which account for the least drug allergies (3.5%).
Insect Bite Allergy
Most people experience a reaction to the venom of an insect bite, which is completely normal.
But people allergic to insect bites tend to experience a more severe reaction than someone who does not suffer from an insect bite allergy.
Insect bite allergy symptoms are mostly limited to the skin and include:
- Pain at sting site
- Swelling beyond the area of the sting
- Skin flushing
Recognizing the symptoms of anaphylaxis is extremely important because this type of severe allergic can impair breathing, cause a drop in blood pressure, and send the body into shock, which can lead to death.
Almost all types of allergies can manifest as anaphylaxis, and the symptoms of anaphylaxis appear suddenly and progress quickly.
Initially, the symptoms of anaphylaxis mimic mild allergic reactions, but over a few minutes progress into the following:
- Breathing difficulties
- Hives and swelling
- Tightness in the throat
- Hoarse voice
- Nausea and vomiting
- Abdominal pain and diarrhea
- Feeling faint and dizzy
- A sharp drop in blood pressure
- Fast heart beat
- Feeling anxious (some describe a feeling of doom)
- Cardiac arrest
People who have experienced an anaphylactic shock are at risk of experiencing the same reaction again.
Treatment involves adrenaline (epinephrine) injection that relaxes the airways and tightens the blood vessels.
As already explained, the immediate cause of allergy is exposure to an allergen.
An allergy is a broad term covering various disease states all characterized by an immune system reacts strongly to a harmless substance such as pollen, dust, and food.
But when speaking of allergies, most people would like to know why exactly their immune system is reacting so strongly to a substance that does not pose a real threat to their health and well-being.
Unfortunately, no one knows the answer to this question, but there are many theories out there giving possible explanations.
Most of these theories suggest that our changing environment and lifestyle has a lot to do with the current rise in allergic disease, which seems to be affecting children more so than adults.
In this section, we cover several theories and the studies behind them to explain the possible underlying cause of allergic disease.
A Faulty Immune System
Research on allergies has been trying to determine for quite some time now the reasons why our bodies seem to become hypersensitive to substances that should normally be completely harmless.
This rather maladaptive bodily reaction seems to show similarities with autoimmune disorders.
For this reason, when trying to develop a plausible allergy hypothesis, most researchers had focused their attention on the immune system.
This makes perfect sense considering that all allergic reactions are controlled by our antibodies, most notably lgE.
The Hygiene Hypothesis
The hygiene hypothesis states that a lack of early childhood exposure to pathogens and substances increases a person’s risk of allergic disease by suppressing the normal development of the immune system.
The hypothesis got its name from the assumption that the higher levels of hygiene practiced in developed countries means that children are not exposed to pathogens as children in less developed countries.
The hypothesis was first established in 1989 by David Strachan.
The idea came from previous research that found that our immune system is partially regulated by the reaction between pathogen and host.
Just consider the example of vaccination, which involves injecting antigens to stimulate the body to develop immunity against the injected pathogen.
However, most allergy experts today believe that the hygiene hypothesis is too simple of an explanation for something as complex as allergic disease and has failed to provide any explanation.
Other Proposed Causes
An article published in the July 2016 issue of the Perspectives in Public Health explains that hygiene has nothing to do with allergy onset.
Instead, the changes in our environment and lifestyle have made it harder for our bodies to adapt and develop a proper immune response to these environmental challenges.
The article suggests that there is some truth to the hygiene hypothesis as far as that our body’s immune system is primarily regulated by the interaction between the microorganisms inside and outside our bodies and our immune system.
Changes in lifestyle due to rising urbanization have changed our levels of exposure to environmental pathogens.
For instance, our diet and excessive antibiotic use have changed the diversity of our gut flora, which also plays an important role in immune system regulation.
Strategies to Help Prevent Allergies In Children
Based on our current knowledge on how our changing environment is wreaking havoc on our immune system, the above-cited article has provided several suggestions that may help support normal immune system functioning.
Natural childbirth, breastfeeding, a more significant interaction between siblings and peers, increasing levels of physical activity and time spent outdoors, reducing the time spent indoors, and reducing antibiotic intake (including that found in food) are just some ways to support the development of a healthy and well-functioning immune system.
Probiotics, organic food, and generally balanced and healthy diets may also help with the development of a healthy immune system and reduced risk of allergies in children.
While research has gone a long way in understanding the mechanisms that trigger allergic reactions, the exact causes of allergy remain largely unknown.
There are, however, certain risk factors may play a role in the development of allergic diseases.
The World Allergy Organization lists several risk factors which the latest research on the allergic disease has recognized in their latest White Book on
For instance, a study that was recently published in Clinical and Translational Allergy has identified specific genes in Dutch children that triggered their allergy to cow’s milk.
The same study also found that these same genes control other types of late-onset allergies, which may explain why children who suffer from milk allergy often develop other allergies later in life.
As research shows, up to 30% of the general population in western countries suffer from allergies.
The most common types of allergies affecting this group are hay fever, asthma, atopic dermatitis, and all are characterized by high sensitivity to allergens that are commonly found in these communities.
Sensitivity to these allergens is confirmed via allergy tests that show the presence of IgE antibodies when exposed to a specific allergen.
What all this means is that allergy is not just a result of a person’s body being hypersensitive to a certain substance but also as a result of that substance invading that person’s living environment.
Indoor and outdoor pollution is considered to be another possible risk factor for allergic disease.
Current research indicates that indoor and outdoor pollution negatively affect respiratory health, and this increases a person’s risk of developing asthma and other allergic diseases.
Pollution from gas fumes, industries, and homes increase the omission of Carbon monoxide, nitrogen dioxide, polycyclic aromatic hydrocarbons, and sulfur dioxide, all of which can be damaging to normal immune system functioning.
Global warming, which is believed to be a result of a rise in global environmental pollution, may also be another contributing factor to the increase of allergic diseases.
An explanation is that global warming causes a rise in airborne pollen, mold, and insects that trigger allergic reactions.
Urbanization and Gut Microbiota
According to an article that was recently published in Experimental and Therapeutic Medicine, children are at a higher risk of developing rhinitis and related allergies when:
- One or both parents suffer from rhinitis
- Living in urban environments with high levels of air pollution
- Inhaling indoor allergens such as dust mites
- Suffering from vitamin D deficiency
- Not interacting with siblings and peers (due to a smaller incidence of viral infections)
Other possible risk factors for allergies include poor gut microbiota.
According to a study published in EBioMedicine, infants with a richer gut microflora had a lesser incidence of food allergies at one year of age when compared to infants with a poor microflora.
A possible explanation for this could lie in the fact that some gut bacteria are known to regulate the production of IgE.
Less gut microbiota is known to cause a rise in IgE while a rise in gut microbiota lowers IgE. The same goes true for some vitamin deficiencies.
Stress as a Risk Factor
Stress is the number one cause of almost all modern diseases is also suggested as another possible risk factor for allergies.
In the past couple of decades, many studies have found links between the nervous, endocrine, and immune system. Furthermore, many allergic diseases were initially thought to be psychosomatic disorders as evident by the fact that early medical text list asthma as “Asthma Nervosa.”
So, it shouldn’t come as surprising than today’s researchers are considering stress as a significant risk factor for allergies as explained in an article published in Immunology And Allergy Clinics of North America.
The article explains that up to 75% of all doctor’s visits are stress-related mostly because stress is known to increase a person’s susceptibility to infections and auto-immune disorders.
Diagnosis and Treatment
There are several treatment options available for allergic diseases with allergy immunotherapy (allergy shots) being the most successful.
Unfortunately, not everyone suffering from allergies has the resources to receive adequate treatment and as noted by WOA, the care for patients with allergies is fragmented and far from ideal.
Most treatment today tends to focus on removing the symptoms without addressing the underlying cause.
The reason for this being that our understanding of allergies is still poor, and future research will hopefully help in the development of effective treatment options.
About Allergy Diagnosis
Currently, addressing allergies involves diagnosis, medication, shots, specialist care, and sublingual immunotherapy.
Diagnosis of allergies is the first step in determining the adequate treatment.
This is because not all allergies are treated with the same remedy.
Diagnosis involves talking to your physician, who will refer you to a specialist called an allergist.
An allergist will first perform a medical history before proceeding to allergy screening. Next, your specialist is likely to perform an allergy skin test.
Allergy skin testing is the gold standard in establishing an allergy diagnosis.
- An allergist will first ask you about your health and whether your family members have had asthma and other allergies.
- Next, they will ask you about your symptoms such as when was the first time you noticed your symptoms, how often, and what do you thing seems to cause these symptoms. They will also ask you about your work, diet, and lifestyle habits to determine the possible causes of your allergic reaction.
- An allergist will perform a general physical exam to check your overall health and how your allergy symptoms are manifesting.
- Your allergist will perform an allergy skin test to test for possible allergies such as pollen, dust, food, insect stings, and other things you were exposed to recently. An allergist needs to narrow down your possible allergens to be able to establish a proper diagnosis.
- The prick test – this test is done on your back or the inside of your arm and involves pricking the surface of your skin with a small concentration of an allergen. In case you are allergic, the area where the allergen was applied will become red.
- The intradermal test – the test involves injecting the allergen into the first few layers of your skin with a fragile needle. This test is used when the prick test comes out clear.
For instance, a blood test may be performed if you are currently taking medication that could interfere with a skin test; if you have susceptible skin which leads to false-positive skin tests, you had a severe reaction to an allergen and exposing you to this allergen again poses a real danger to your health and well-being.
A blood test is performed by drawing out a blood sample and sending it to the lab to look for specific antibodies for a certain allergen. The test takes several days to complete.
Once your allergist determines what it is exactly what you are allergic to, then the first in line treatment involves avoiding that substance.
As simple as it sounds, avoiding allergens when you can maybe the best way to prevent a future allergic reaction.
However, there are instances when someone cannot avoid an allergen as in the case of seasonal pollen allergy.
In such cases, medication is required to suppress the symptoms and improve a person’s functioning and well-being.
These medications reduce symptoms such as a runny nose, sneezing, and itching. Medication used in the treatment of common allergies includes:
Corticosteroids – these are a class of drugs that reduce inflammation and are usually prescribed to people with allergies affecting the air passages.
Allergies treated with corticosteroids include asthma, pollen, dust, and mold allergies.
Antihistamines – antihistamines come in pill, nasal spray, liquid, or as eye drops.
They are also sold as over-the-counter medicine, but some can only be obtained through a doctor’s prescription.
Antihistamines work by suppressing histamine production by mast cells.
During an allergic reaction, histamine attaches to receptors in your blood vessels, which causes them to enlarge, and this leads to symptoms such as congestion, itchiness, and increased secretions.
Bronchodilators – commonly sold under the trade names like Ventolin, Proventil, and Xopenex, these drugs help control asthma symptoms and bronchitis.
Bronchodilators are substances that dilate the bronchi that tighten during an asthma attack.
< strong>Mast Cell Stabilizers – Another asthma medication, mast cell stabilizers help treat inflammation in the bronchial tubes, but they also help treat other allergies affecting the eyes and nose.
These drugs may need to be taken for several weeks before they start showing any results.
These drugs also work by suppressing the release of histamine from mast cells.
While most allergy medication only suppresses the symptoms and provides short-term relief, allergy shots help with treating allergies in the long run.
Also called subcutaneous immunotherapy (SCIT), allergy shots change your immune system and prevent and treat allergies.
The treatment involves injecting an extract from the allergen into the skin.
At first, you are to receive an injection every week for up to 7 months after which you may need to take the therapy for every other week for a couple of more months or even up to five years.
Although the treatment is rather lengthy, the efficiency of this form of therapy in completely eradicating the allergy is now confirmed.
A newer variation of this form of therapy was recently introduced and is called Sublingual immunotherapy (SLIT).
The treatment involves administering small doses of a specific allergen under the tongue instead of injecting it into the skin as with SCIT.
Since most people are allergic to more than one substance at once, they will probably be administered with more allergens to provide relief from all allergies.
Although generally considered safe, allergy shots do come with their own risks in rare cases.
An anaphylactic shock from allergy shots does happen, which is why this therapy needs to be administered under the careful surveillance of an allergist.
Other Advantages Of Taking Allergy Shots
While becoming resilient to an allergy is definitely good news, newer studies have discovered a new type of hepatitis B vaccine thanks to allergy immunotherapy.
A study published in EBioMedicine last September states that a more efficient vaccine against the hepatitis B virus was developed from immunotherapy for different types of allergies.
This type of vaccine apparently helps with the development of potent antibodies that fight off the hepatitis virus.
Because allergy therapy is considered to be generally safe, future research on this form of therapy may happen to discover further advantages of therapies that help strengthen our immune system against common diseases.
As much as 30% of the world’s population is believed to be suffering from allergies, but research on allergies is still far away from discovering the exact causes of allergies.
While we already know that allergies are a result of our immune system reacting to a substance that is in normal circumstances completely harmless, we don’t really understand why this type of maladaptive reaction happens in the first place.
Proposed theories include variations of the “hygiene hypothesis” that suggest that environmental and lifestyle changes that took place in the past 100 years have weakened our immune system.
A poor functioning immune system is already known to lead to various disease states such as autoimmune disorders, and researchers believe this may also be the case with allergies.
Being exposed to more allergens during childhood may not be enough to prevent allergies, but it may reduce a child’s risk of developing allergies at least to some degree.
Eating a healthy diet, living a healthy lifestyle, and taking antibiotics are just a couple of standard measures that could help prevent allergic diseases.
People may also control certain risk factors that are strongly linked to allergies such as environmental pollution, antibiotic intake, vitamin D deficiencies, and similar.
But other risk factors such as a strong family history of allergies may be hard to control. Allergies tend to run in the family, and certain regions are more likely to have higher allergy incidences than others.
While moving to another place may be an excellent way to reduce your risk of developing allergies, this is simply not possible for most people as their work and life obligations are bound to a specific place.
Nevertheless, spending more time outdoors in non-polluted areas can prove to be helpful.
Until researchers find what exactly is the cause of the onset of allergies like asthma, hay fever, peanut allergies, insect sting allergies, and others, may need to continue taking their medication.
Treatment of allergies starts with the proper diagnosis.
Once you know what it is exactly what you are allergic to, your first-in-line treatment involves avoiding the allergen.
When you cannot avoid the allergen because it is merely present in the environment where you live, you may benefit from taking drugs like corticosteroids, antihistamines, and mast cell stabilizers to help with your symptoms.
Relieving your stress levels is another way to bring allergies under control.
But the most successful treatment option for allergies today is subcutaneous immunotherapy which can help you stop being allergic to a specific allergen.
Although this form of therapy is rather lengthy, expensive, and challenging to adhere to, it is the only method proven to eradicate allergies completely.
People whose allergies are causing problems in their health and functioning may benefit from talking to a doctor about this treatment option.