What is an Allergy?

The prevalence of allergic diseases worldwide is rising dramatically in both developed and developing countries. A steady increase in the prevalence of allergic diseases globally has occurred with about 30-40% of the world population now being affected by one or more allergic conditions.

According to World Health Organization (WHO) statistics, hundreds of millions of subjects in the world suffer from rhinitis and it is estimated that more than 300 million have asthma, markedly affecting the quality of life of these individuals and their families, and negatively impacting the socio-economic welfare of society. It is forecast that allergic problems will increase further as air pollution and the ambient temperature increase. These environmental changes will affect pollen counts, the presence or absence of stinging insects, and the presence or absence of molds associated with allergic diseases.

These diseases include asthma; rhinitis; anaphylaxis; drug, food, and insect allergy; eczema; and urticaria (hives) and angioedema. This increase is especially problematic in children, who are bearing the greatest burden of the rising trend which has occurred over the last two decades.

Allergies are one of the most common chronic diseases. An allergy is an abnormal reaction to a harmless substance called an allergen. An allergen means a substance that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body, such as pollens, foods, and house dust mite. This allergic reaction is due to a mistake of the immune system. The immune system protects us against invasion by harmful external agents such as bacteria or viruses that can cause infections, or own cells, such as tumor cells.

But it must also be able to allow the entry of beneficial substances as the nutrients ingested with food. Allergens are tolerated without problems by non-allergic individuals. Most people have no problems being in contact with pets like cats, but when you are allergic to them you start to sneeze, you get an itchy and runny nose and red and itchy eyes.

Symptoms of Allergies

An allergic reaction begins when an allergen enters the body, triggering an antibody response. When the allergen comes into contact with the antibodies, these cells respond by releasing certain substances including histamine. These substances cause the symptoms. The symptoms of an Allergy are like an alarm signal, warning that something is wrong.

Common symptoms associated with allergic conditions include:

  • sneezing
  • wheezing
  • sinus pain
  • runny nose
  • coughing
  • nettle rash / hives
  • swelling
  • itchy eyes, ears, lips throat and mouth
  • shortness of breath
  • sickness, vomiting & diarrhea
  • increase in nasal and airway secretions

Any of these symptoms can be caused by other conditions, none of these symptoms are exclusive of allergy and some of them can be very serious. If you suffer from them we recommend you to visit a doctor.

Sneezing helps clearing the airways from substances identified as harmful. This is associated to allergic disorders such as rhinitis, hay fever and anaphylaxis.

Nose itching is an alarm signal warning that something is going wrong in our nose.

Nasal blockages can happen when there is an obstruction due to mucus secretion, to the inflammation of the nose or to the growth of nasal polyps.

Nose mucus is the mucus in the nose, necessary to catch and neutralize harmful. The mucus in the nose can be liquid or thick, transparent or colored.

Swelling is due to the flow of liquid from the blood vessels to the deeper layers of the skin.

Eye itching is an alarm signal, warning that something is going wrong in our eyes.

Eye redness or dilation of blood vessels in the surface of the eyeballs leads to eye redness.

Coughing helps to clear the airways from secretions or foreign particles such as allergens and microbes.

Chest tightness is the feeling of a pressure of the chest, that causes difficult breathing. You feel that sensation, if the airways are narrowed and the air cannot pass easily.

Shortness of breath or breathlessness is associated to disorders such as asthma and anaphylaxis. It is difficult to inhale or exhale air. It is a warning signal. You can have this feeling if you try to breathe through a straw.

Headache caused by nasal congestion or the blockage of mucus secretion in the sinuses can lead to headache.

Diarrhea is often associated to allergic disorders such as food allergy and anaphylaxis. Food that has not been digested or an accelerated transit of the food in the bowels can lead to liquid stools.

Abdominal pain is caused when the digestive system is not functioning correctly and you feel a pain in the belly, often associated to vomiting or diarrhea.

Vomiting has the objective of getting rid of a content that the organism identifies as harmful. It occurs at allergic disorders such as food allergy and anaphylaxis.

Wheezing is when the air passes through a narrowed or obstructed airway a whistling sound is produced during breathing. This is called “wheezing”. This is associated with asthma.

Skin redness is often associated with atopic dermatitis or contact dermatitis. Skin redness appears, when the blood vessels are dilated due to harmful stimuli.

Skin itching is always a signal that something is wrong. Receptors in the skin are stimulated and are the cause, why we want to scratch. (atopic dermatitis, contact dermatitis)

Causes of Allergies

Real allergies are almost always triggered by large protein molecules. Proteins that are known to have the capacity to cause allergies are called allergens. Substances in the environment known as allergens are triggers of an allergic reaction. Nearly anything can be an allergen for someone.
The most common causes of allergies are:

Types of Allergies

Allergies are classified into IgE mediated and non-IgE mediated allergies.

IgE mediated allergy

In IgE mediated allergy the immune system produces great amounts of a class of antibodies known as IgE antibodies that are, specific for the particular offending allergen. These IgE antibodies bind to the surface of cells in the body called “mast cells” which become IgE-sensitized. These cells can then identify particular allergens the next time they come in contact with the body. This process is called sensitization, and at this stage there are no physical symptoms of an allergy.

Mast cells are present in the skin, eyes, nose, mouth, throat, stomach and gut. The next time that we get in contact with the same allergen the mast cells identify it as an enemy and produce histamine and other chemicals. The release of these substances from mast cells induces the allergic symptoms. In the nose histamine release results in symptoms of runny nose, itchy nose, sneezing that are commonly associated with itchy red eyes.

In the skin symptoms include redness and nettle rash. In the breathing tubes allergies cause wheezing, cough and shortage of breath, whereas in the gut symptoms such as abdominal discomfort, nausea, vomiting and diarrhea may occur. Severe allergic reactions are also known as anaphylaxis, and can be life-threatening.

Non-IgE mediated allergy

Non-IgE-mediated reactions, which are poorly defined both clinically and scientifically, are believed to be T-cell-mediated. This mechanism is related to disorders such as contact eczema (allergic contact dermatitis). Whereas symptoms of IgE mediated allergies occur rapidly and soon after exposure to the allergen, this may not be the case with non-IgE mediated allergies where symptoms may appear much later, usually 24-48 h.

Acute response: this is what we usually call allergy. The immediate reaction occurs within 15 – 30 minutes of exposure to the allergen. During the early phase reaction chemical mediators released by mast cells including histamine, prostaglandins, leukotrienes and thromboxane produce local tissue responses characteristic of an allergic reaction. In the respiratory tract for example, these include sneezing, edema and mucus secretion, with vasodilatation in the nose, leading to nasal blockage, and bronchoconstriction in the lung, leading to wheezing.

Late-phase response: Occurs 4-6 hours after the disappearance of the first phase symptoms and can last for days or even weeks. During the late phase reaction in the lung, cellular infiltration, fibrin deposition and tissue destruction resulting from the sustained allergic response lead to increased bronchial reactivity, edema and further inflammatory cell recruitment. These observations suggest that IgE is instrumental in the immune system’s response to allergens by virtue of its ability to trigger mast cell mediator release, leading directly to both the early and late phase reactions.


Which elements are involved in the allergic reaction:

Allergen Usually a protein, that can generate an allergic reaction.

Immunoglobulin (IgE) An antibody involved in allergic reactions.

Mast cell Are immune system cells which are located in the skin, respiratory tract and digestive tract. IgE molecules are attached to their surface. Histamine and other mediators are produced by mast cells, which are released during the allergic reaction inducing allergy symptoms.

Histamine Is stored within the mast cell and released during the allergic reaction. Has the ability to dilate blood vessels (vasodilation), increase permeability of blood vessels (fluid leak) and stimulates the nerves. This results in redness, swelling and itching.

Allergy Diagnosis & Testing

Do you sneeze every time you pet a cat? Do you break out in hives when a bee or wasp stings you? Then you may already know what some of your allergens are. Very often you don’t know what is causing your allergy symptoms. Diagnosing allergy can be difficult since the symptoms may be similar to other conditions. You may be referred by your GP to an allergy specialist.

Doctors diagnose allergies in three steps:

  1. Personal and medical history
    Your doctor will ask you lots of questions to find out the possible causes of your clinical symptoms. Make notes at home about your family history, the kinds of medicines you take, and your lifestyle at home, school or work. Write down when, where and how symptoms occurred. Do you only get symptoms at certain times of the year? Do you suffer more at night time or during the day? Does exposure to animals bring on your symptoms? Do they occur at any particular time of the day? Does any food or drink bring on your symptoms. This will help the doctor to get a complete understanding of your symptoms.
  2. Physical exam
    If there is evidence of allergy your doctor will have a look at your eyes, nose, ears, throat, chest and skin during the exam. In some cases the doctor has to check your lungs with a pulmonary function test. Sometimes you also may need an X-ray of your lungs or sinuses.
  3. Tests to determine your allergens
    Tests are just one of many tools available to assist your doctor in making a diagnosis. No one test alone is able to diagnose an allergy. There are a variety of tests that doctors use to diagnose allergies, so each experience may be different.

Management of Allergy

The first and most important step in the management of Allergy is allergen avoidance. Preventing exposure to allergens is the key to managing allergies. A health professional can advise on avoiding allergens specific to your situation.

Drugs are effective in the control and treatment of allergic diseases but do not cure the underlying allergy. Mostly a combination of two approaches will result in significant improvement in allergic symptoms.

  1. Reducing the risk of an allergic reaction by avoiding the allergen, wherever possible.
  2. Medical treatments to reduce symptoms including medications and immunotherapy.

Most allergic reactions are mild and do not cause life-threatening reactions, although they can be very troublesome for the patient. A small number of people may experience a severe allergic reaction called anaphylaxis.

When you cannot avoid allergens, there are many medicines that can help control allergy symptoms. Decongestants and antihistamines are the most common allergy medications. They help to reduce a stuffy nose, runny nose, sneezing and itching. Other medications work by preventing the release of the chemicals that cause allergic reactions. Corticosteroids are effective in treating inflammation in your nose. These treatments control the symptoms and reactions; they do not cure the condition.

Medication for the Management of Allergy


What is anaphylaxis?

Anaphylaxis is a severe, potentially life-threatening allergic reaction. It can occur within seconds or minutes of exposure to something you’re allergic to. The most common anaphylactic reactions are to foodsinsect stings and medications.

If you are allergic to a substance, your immune system overreacts to this allergen by releasing chemicals that cause allergy symptoms. Typically, these bothersome symptoms occur in one location of the body. However, some people are susceptible to a much more serious anaphylactic reaction. This reaction typically affects more than one part of the body at the same time. The flood of chemicals released by your immune system during anaphylaxis can cause you to go into shock; your blood pressure drops suddenly and your airways narrow, blocking normal breathing.


Signs and symptoms of anaphylaxis can occur within seconds or minutes of exposure to something you’re allergic to:

  • Skin reactions, including hives along with itching
  • Flushed or pale skin
  • A feeling of warmth
  • The sensation of a lump in your throat
  • Wheezing, shortness of breath, throat tightness, cough, hoarse voice, chest pain/tightness, trouble swallowing, itchy mouth/throat, nasal stuffiness/congestion
  • A weak and rapid pulse
  • Nausea, vomiting or diarrhea
  • Dizziness
  • Headache
  • Anxiety
  • Low blood pressure
  • Loss of consciousness

The most dangerous symptoms are low blood pressure, breathing difficulty and loss of consciousness, all of which can be fatal. If you have any of these symptoms, particularly after eating, taking medication or being stung by an insect, seek medical care immediately. DON’T WAIT !!!!!

Anaphylaxis requires immediate medical treatment, including an injection of adrenalin and follow up medical examination in a hospital emergency room.



Any food can cause an allergic reaction. Foods that cause the majority of anaphylaxis are peanuts, tree nuts (such as walnut, cashew, Brazil nut), shellfish, fish, milk, eggs and preservatives.

Stinging insects

Insect sting venom from, honeybees, wasps or yellow jackets, hornets and fire ants can cause severe and even deadly reactions in some people.


Common medications that cause anaphylaxis are antibiotics (such as penicillin) and anti-seizure medicines. Certain blood and blood products, radiocontrast dyes, pain medications and other drugs may also cause severe reactions.

Less common causes


Natural latex products contain allergens that can cause reactions in sensitive individuals.


Very rare, exercise can cause anaphylaxis. In some cases it is seen after eating certain foods before exercise.

If you have allergies or asthma and have a family history of anaphylaxis, your risk is higher. Even if you or your child has had only a mild anaphylactic reaction in the past, there’s still a risk of more severe anaphylaxis.


Your doctor will ask you questions about your allergies or any previous allergic reactions you’ve had:

  • Whether any particular foods seem to cause a reaction
  • Whether stings from any particular type of insect seem to cause your symptoms
  • Any medications you take, and if certain medications seem linked to your symptoms
  • Whether you’ve had allergy symptoms when your skin has been exposed to latex

Then you may be tested for allergies with skin tests or blood tests and your doctor may also ask you to keep a detailed list of what you eat or to stop eating certain foods for a time

Other conditions as a possible cause of your symptoms have to be excluded, like:

  • Seizure disorders
  • Mastocytosis, an immune system disorder
  • Non-allergic conditions that causes skin symptoms
  • Psychological issues
  • Heart or lung problems


During an severe anaphylactic reaction, an emergency medical team may perform cardiopulmonary resuscitation if you stop breathing or your heart stops beating. They will give you medications:

  • Epinephrine (adrenaline) to reduce your body’s allergic response
  • Antihistamines and cortisone (intravenous) to reduce inflammation of your air passages and improve breathing
  • A beta-agonist (e.g. albuterol/salbutomol) to relieve breathing symptoms
  • Oxygen

If you are at risk of anaphylaxis your allergist may prescribe autoinjectable epinephrine/adrenaline. This device (“Pen”) is a combined syringe and concealed needle that injects a single dose of epinephrine/adrenaline when pressed against your thigh. Make sure you understand how and when to use it. Also, make sure the people closest to you (family, colleagues, employers and school staff) know how to use the adrenaline pen, maybe one of them could save your life. Always refill the prescription upon expiration. There are no special storage conditions. Do not let it freeze (0°C). When flying: You may carry the pen in your hand luggage. Security and flight personnel may not know this, therefore ask your doctor to give you a signed travel certificate. This medication (“Pen”) must be carried with you at all times.


In some cases, your allergist may suggest specific treatments, such as immunotherapy (allergy shots) to reduce your body’s allergic response to insect stings. Immunotherapy, also known as desensitization or hypo-sensitization is the best treatment option for people who are allergic to stinging insects as it can reduce the risk of a future severe reaction to less than 5%. Venom immunotherapy is given in the form of shots, and about 80 to 90% of patients who receive it for 3 to 5 years do not have a severe reaction to a future sting.

What can you do to prevent a future attack?

In most other cases there’s no way to treat the underlying immune system condition that can lead to anaphylaxis.

  • Avoid your known allergy triggers as much as you can
  • If prescribed by your doctor, carry self-administered epinephrine/adrenaline Pen always with you. During an anaphylactic attack, you can give yourself the drug using the Pen (e.g. EpiPen, Jext, Emerade).
  • If you feel the symptoms, don’t wait, use the pen.
  • Your doctor also may recommend taking corticosteroid and/or antihistamine tablets.

In all cases do not forget to dial emergency number and call for help.