What are allergies? What is an allergy?
Allergies are hypersensitive immune responses to substances that either enter or come in contact with the body, such as pet dander, pollen or bee venom. A substance that causes an allergic reaction is called an "allergen". Allergens can be found in food, drinks or the environment.
Most allergens are harmless, i.e. the majority of people are not affected by them.
If you are allergic to a substance, such as pollen, your immune system reacts to it as if it were a pathogen (a foreign harmful substance), and tries to destroy it.
Allergies are very common. Public health authorities estimate that about 20% of people in North America and Western Europe suffer from some degree of hay fever (allergic rhinitis, allergy to pollen).
A study published in JAMA Pediatrics (September 2013 issue) reported that kids' food allergies cost both families and the US as a whole nearly $25 billion annually.
The number of people worldwide with allergies is increasing. According to Allergy UK, about 30% to 40% of people have an allergy at some stage in their lives. Some years ago, this increase was only apparent in industrialized nations. However, middle-income nations are now reporting higher rates of allergies across their populations.
The steepest increase in allergies has been observed in children, particularly food allergies.
A team of researchers from Northwestern University Feinberg School of Medicine reported in Pediatrics that about 8% of American children have some kind of food allergy. 38.7% of those with food allergies have a history of anaphylaxis (severe allergic reactions), and 30.4% are allergic to more than one food.
Researchers from St. Luke's Roosevelt Hospital Center, New York, found that foreign-born children who live in the USA have a lower risk of allergies. This risk grows the longer they remain in America.
What are the signs and symptoms of allergies?
A symptom is something the patient feels and describes, while a sign can be detected by others too. Pain is a symptom and a rash is a sign.
When a person with an allergy comes into contact with an allergen, the allergic reaction is not immediate. The immune system gradually builds up sensitivity to the substance before overreacting to it.
The immune system needs time to recognize and remember the allergen. As it becomes sensitive to it, it starts making antibodies to attack it - this process is called sensitization.
Sensitization can take from a few days to several years. In many cases the sensitization process is not completed and the patient experiences some symptoms but never a full allergy.
When the immune system reacts to an allergen, there is inflammation and irritation. Signs and symptoms depend on the type of allergen. Allergic reactions may occur in the gut (digestive system), skin, sinuses, airways, eyes, and nasal passages.
Allergies from dust and pollen may have the following symptoms:
Blocked noseItchy eyesItchy noseRunny noseSwollen eyesWatery eyesCough.
Skin reactions, as in eczema (atopic dermatitis) may include:
Flaking skinItchy skinPeeling skinRed skin, rashes.
Food allergies may include several types of reactions:
VomitingTongue swellingTingling in the mouthSwelling of the lipsSwelling of the faceSwelling in the throatStomach crampsShortness of breathRectal bleeding (in children, rare in adults)Itchiness in the mouthDiarrheaAnaphylaxis - a very severe, often life-threatening allergic reaction.
The following allergic reactions are possible after an insect sting:
WheezingSwelling where the sting occurredSudden drop in blood pressureSkin itchingShortness of breathRestlessnessHives - a red and very itchy rash that spreadsDizzinessCoughChest tightnessAnxietyAnaphylaxis.
The following may be signs of an allergic reaction to medication:
WheezingSwollen tongueSwollen lipsSwelling of the faceSkin rashItchinessAnaphylaxis.
Signs and symptoms of anaphylaxis
Anaphylaxis is a serious allergic reaction of rapid onset. Anaphylaxis can be life-threatening and must be treated as a medical emergency.
This type of allergic reaction presents several different symptoms which 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.Anaphylaxis is a medical emergency
Researchers from the University of Manitoba, Canada, reported in The Journal of Allergy & Clinical Immunology that the most commonly affected areas in anaphylaxis are the skin (80-90%), respiratory (70%), gastrointestinal (30-45%), cardiovascular 10-45%) and the central nervous system (10-15%). In most cases two areas are affected simultaneously.
Anaphylaxis - skin symptoms
Hives all over the body, flushing and itchiness. The affected tissues may also become swollen (angioedema). Some patients may experience a burning sensation on the skin.
In about 20% of cases, there is swelling of the tongue and throat.
If the skin has a strange bluish color, it could be a sign of hypoxia (lack of oxygen).
Some patients may experience a runny nose. The membrane that covers the front of the eye and the inside of the eyelid (conjunctiva) may become inflamed.
Anaphylaxis - respiratory symptoms:
Shortness of breathWheezing - caused by bronchial muscle spasmsStridor - a high-pitched vibrating wheezing sound when breathing. Caused by upper airway obstruction due to swellingHoarsenessOdynophagia - pain when swallowingCough.
Anaphylaxis - cardiovascular symptoms
Coronary artery spasm - sudden tightening of the muscle in the artery wall (temporary) due to cells in the heart that release histamine. This can lead to myocardial infarction (heart attack), dysrhythmia (abnormal heart rhythm), or cardiac arrest (heart stops).
Low blood pressure can cause the heart rate to accelerate. In some cases a slow heart rate can occur as a result of low blood pressure (Bezold-Jarisch reflex).
Patients whose blood pressure suddenly drops can feel lightheaded and dizzy. Some may lose consciousness. In some rare cases, the only sign of anaphylaxis might be low blood pressure.
Anaphylaxis - gastrointestinal symptoms
Abdominal crampsDiarrheaVomitingLoss of bladder controlPelvic pain (like uterine cramps).
Patients may also have a sense of impending doom.
What are the causes of allergies?
The immune system of a person with an allergy reacts to the allergen as though it were a harmful pathogen - such as an undesirable bacterium, virus, fungus or toxin. However, the allergen is not harmful. The immune system has simply become oversensitive to that substance.
When the immune system reacts to an allergen, it releases immunoglobulin E (IgE), a type of antibody. IgE is released to destroy the allergen. IgE causes chemicals in the body to be produced. These chemicals cause the allergic reaction.
One of these chemicals is called histamine. Histamine causes tightening of the muscles, including those in the airways and the walls of blood vessels. It also makes the lining of the nose produce more mucus.
People with allergies blame the allergen for their symptoms - a friend's pet, pollen or dust mites. However, the allergens are not harmful. The problem is not the allergen but the allergic person's immune system which mistakes harmless substances for harmful ones.
What are the risk factors for allergies?
In medicine, a risk factor is something that raises the risk of developing a disease or condition. This risk can come from something a person does. For example, smoking is a risk factor for lung disease. It can also be something you are born with. For example, if your mother had breast cancer, her daughter has a higher risk of developing breast cancer too. A family history of breast cancer is a risk factor.
Below are some risk factors associated with allergies:
A family history of asthma - if your parents, grandparents or siblings have/had asthma, your risk of having an allergy is higher.
A family history of allergies - if a close relative has/had an allergy, your risk of having an allergy yourself is greater.
Being a child - a child is much more likely to have an allergy than an adult. On a positive note, this means that many children outgrow their allergies.
Having asthma - people with asthma are significantly more likely to develop allergies.
Not enough sunlight exposure - scientists from the European Centre for Environment & Human Health, together with researchers from various Australian centers found that children living in areas with less sunlight had higher rates of allergies.
Having an allergy - if you already have an allergy, there is a greater risk that you will develop an allergy to something else.
C-section babies - a team from the Henry Ford Hospital reported that C-section babies have a considerably higher risk of developing allergies compared to those born naturally.
Chemicals used in water purification - Elina Jerschow, M.D., M.Sc., a fellow of the American College of Allergy, Asthma and Immunology, said that pesticides in tap water could be partly to blame for the increased food allergy rates in the USA.
What are the most common allergens?
An allergen is a substance which causes an allergic reaction in some susceptible people.
Below are the most common allergens, apart from foreign proteins found in blood transfusions and vaccines:
Allergens from animals
Dust mites - their excrementCockroaches calyxWoolFurDander - skin flakes (dandruff)Fel d 1 - a protein found in cat saliva and sebaceous glands. Proteins from the urine, saliva or hair of household pets can cause allergic reactions in some people.
Medications
PenicillinSalicylates - a salt of salicylic acid commonly found in many medications, including aspirinSulfonamides
Foods - theoretically, any food can cause an allergy. The eight foods most likely to cause allergies are eggs (especially egg-white, albumen), fish, milk, nuts from trees, peanuts (groundnuts), wheat, soy, and shellfish.
Scott H. Sicherer, MD, Professor of Pediatrics, Jaffe Food Allergy Institute at Mount Sinai School of Medicine, and colleagues reported in the Journal of Allergy and Clinical Immunology that the number of kids with peanut allergies more than tripled between 1997 and 2008.
The following foods can also cause allergies:
Corn (maize)CeleryPumpkinBeansSesame.
Insect stings
wasp sting venommosquito stingsbee sting venomfire ants.
Insect bites
kissing bugshorsefliesfleasblackflies.
Insects that cause respiratory allergies
cockroachescaddis flieslake fliesmidgesmoths.
Mold spores
AlternariaAspergillusAureobasidium (Pullularia)Cladosporium (Hormodendrum)EpicoccumFusariumHelmin thosporiumMucorPenicilliumRhizopus.
Plant pollens - cause hay fever.
grass - the most common cause of hay fevertrees - including oak, ash, cedar, willow, and hazelweeds - such as mugwort and ragweed.
Other allergens
household chemicalsmetal - nickel, cobalt, chromium, and zinclatex.
Diagnosing allergies
The doctor will ask the patient questions regarding the allergy symptoms, when they occur, how often and what seems to cause them.
The patient will also be asked whether there is a family history of allergies, and whether other household members (who might not be relatives) have allergies.
The doctor, probably a primary care physician initially, may either recommend some tests to find out which allergen is causing the symptoms, or refer the patient to a specialist.
In the American College of Allergy, Asthma and Immunology's website there is a page called "Find an Allergist", where you can find a specialist who has been certified by the College.
On The British Society for Allergy & Clinical Immunology: BSACI homepage you can find an allergy clinic near you (UK only).
Even if the patient knows what causes his/her allergy, the doctor will wish to carry out tests to determine whether a particular substance within the food, drink, or something else is the culprit.
Below are some examples of allergy tests
Blood test - to measures levels of IgE antibodies released by the immune system. This test is sometimes called the radioallergosorbent test (RAST).
Skin prick test - also known as puncture testing or prick testing. The skin is pricked with a small amount of a possible allergen. If there is a skin reaction - itchy, red and swollen skin - it may mean there is an allergy.
Patch test - for patients with contact dermatitis (eczema). Special metal discs with trace amounts of a suspect allergen are taped onto the back. The doctor checks for a skin reaction 48 hours later, and then again after a couple of days.
The National Health Service says that commercial allergy-testing kits are not recommended and that patients should have these tests done by specialized health care professionals.
The National Institute for Health and Clinical Excellence (NICE), in the UK, found that the IgE antibody test and the skin prick test were cost effective compared with no test.
What are the treatment options for allergies?
The most effective treatment and management of an allergy is to avoid exposure to the allergen.
However, sometimes it is not possible to completely avoid an allergy. A person with hay fever cannot avoid exposure to pollens, unless he/she closes all the windows in the house and never goes out. Even then, there is a risk of other people bringing pollen into the house.
It is also important to educate patients so that they know how to identify their allergenic foods properly. Many people with peanut or tree nut allergy could not correctly identify which items they were allergic to in a study carried out at Ohio State University.
Study leader, Professor Todd Hostetler, said "When we ask patients to avoid peanuts and tree nuts, we shouldn't assume patients know what they're looking for, because they may not. It's worthwhile to do some education about what a tree nut is, what a peanut is, and what they all look like."
Medications for allergies
Drugs can help treat the symptoms of allergy, but do not cure it. The majority of allergy medications are OTC (over-the-counter, no prescription required). Before considering a medication, speak to a pharmacist or your doctor.
Antihistamines (histamine antagonists) - they block the action of histamine, a chemical released in the body as part of an allergic reaction. Some antihistamines are not suitable for children.
Decongestants - some patients say they help with a blocked nose in cases of hay fever, pet allergy or dust allergy. Decongestants are short-term medications.
Leukotriene receptor antagonists (anti-leukotrienes) - for asthma when other treatments have not worked. Anti-leukotrienes block the effects of leukotrienes, chemicals that cause swelling. Leukotrienes are released in the body when there is an allergic reaction.
Steroid sprays - applied to the inside lining of the nose. Corticosteroid sprays help reduce nasal congestion.
Immunotherapy
Also known as hyponsesitization. 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 allergen's tendency to trigger IgE production.
Immunotherapy is only used in cases of severe allergies.
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