Allergy (Allergies) Causes, Types, Symptoms, Diagnosis, Treatment, Prevention,Home Remedies

Allergy (Allergies) Causes, Types, Symptoms, Diagnosis, Treatment, Prevention,Home Remedies

What are Allergy (Allergies)?

Allergies are the immune system’s inappropriate response to a foreign substance. Exposure to what is normally a harmless substance, such as pollen, causes the immune system to react as if the substance were harmful. Substances that cause allergies are called allergens. Most allergies result from a combination of inheritance (genes) and environmental exposures (pollens, animal danders, etc.). Being exposed to allergens at certain times when the body’s defenses are low or weak, such as after a viral infection or during pregnancy, also may contribute to the development of allergies.

Allergy (Allergies) Causes, Types, Symptoms, Diagnosis, Treatment, Prevention,Home Remedies

Your immune system produces substances known as antibodies. Some of these antibodies protect you from unwanted invaders that could make you sick or cause an infection. When you have allergies, your immune system makes antibodies that identify a particular allergen as something harmful, even though it isn't. When you come into contact with the allergen, your immune system's reaction can inflame your skin, sinuses, airways or digestive system.

When you come into contact with an allergen, you may experience symptoms of allergic rhinitis (hay fever) including sneezing, congestion, itchy, watery nose and eyes and/or asthma symptoms such as wheezing, chest tightness, difficulty breathing and coughing.

Allergic disorders affect an estimated 1 in 5 adults and children (40 to 50 million people) and are the sixth leading cause of chronic illness in the United States, according to the Allergy Report from the American Academy of Allergy, Asthma and Immunology (AAAI).

The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis — a potentially life-threatening emergency. While most allergies can't be cured, a number of treatments can help relieve your allergy symptoms.

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What Causes Allergy (Allergies)

An allergy develops when the body’s immune system reacts to an allergen as though it is harmful, like it would an infection.

It produces a type of antibody (protein that fights off viruses and infections) called immunoglobulin E (IgE) to fight off the allergen.

When the body comes into contact with the allergen again, IgE antibodies are released, causing chemicals to be produced. Together, these cause the symptoms of an allergic reaction.

One of the chemicals involved in an allergic reaction is histamine, which causes:

  • tightening of your muscles, including those in the walls of your airways
  • more mucus to be produced in your nose lining, causing local itching and burning

Common allergens

An allergen is any substance that causes your body’s immune system to overreact and produce antibodies against it.

There are thousands of allergens that can trigger allergies, but some of the most common include:

  • house dust mites
  • grass and tree pollens
  • pet hair or skin flakes
  • fungal or mould spores
  • food (particularly milk, eggs, wheat, soya, seafood, fruit and nuts)
  • wasp and bee stings
  • certain medication, such as penicillin
  • latex
  • household chemicals

Who is at risk for Allergy (Allergies) and why?

Allergies can develop at any age, and the initial exposure or sensitization period may even begin in the womb. Individuals can also outgrow allergies over time. Whereas many children outgrow food allergies, nasal or environmental allergies are something that individuals often grow into over time, often into young adulthood.

Allergy (Allergies) Causes, Types, Symptoms, Diagnosis, Treatment, Prevention,Home Remedies

Why, you may ask, are some people "sensitive" to certain allergens while most are not? Why do allergic persons produce more IgE than those who are nonallergic? Although we certainly do not fully understand why one person develops allergies and another does not, we know there are several risk factors for allergic conditions. Family history, or genetics, plays a large role, with a higher risk for allergies if parents or siblings have allergies. There are numerous other risk factors for developing allergic conditions. Children born via Cesarean section have a higher risk of allergy as compared to children who are delivered vaginally. Exposure to tobacco smoke increases the risk of allergy. Boys are more likely to be allergic than girls. Exposures to antigens, use of antibiotics, and numerous other factors, some of which are not yet known, also contribute to the development of allergies. This complicated process continues to be an area of medical research.

Symptoms of Allergy (Allergies)

Allergy symptoms depend on your particular allergy, and can involve the airways, sinuses and nasal passages, skin, and digestive system. Allergic reactions can range from mild to severe. In some severe cases, allergies can trigger a life-threatening reaction in your body known as anaphylaxis.

Hay fever

Hay fever, also called allergic rhinitis, may cause:

  • Congestion
  • Itchy, runny nose
  • Itchy, watery or swollen eyes (conjunctivitis)

Atopic dermatitis

Atopic dermatitis, an allergic skin condition also called eczema, may cause:

  • Itchy skin
  • Red skin
  • Flaking or peeling skin

A food allergy

A food allergy may cause:

  • Tingling mouth
  • Swelling of the lips, tongue, face or throat
  • Hives
  • Anaphylaxis

An insect sting allergy

An insect sting allergy may cause:

  • A large area of swelling (edema) at the sting site
  • Itching or hives all over your body
  • Cough, chest tightness, wheezing or shortness of breath
  • Anaphylaxis

A drug allergy

A drug allergy may cause:

  • Hives
  • Itchy skin
  • Rash
  • Facial swelling
  • Wheezing
  • Anaphylaxis


Some types of allergies, including allergies to foods and insect stings, have the potential to trigger a severe reaction known as anaphylaxis. A life-threatening medical emergency, this reaction can cause you to go into shock. Signs and symptoms of anaphylaxis include:

  • Loss of consciousness
  • Lightheadedness
  • Severe shortness of breath
  • A rapid, weak pulse
  • Skin rash
  • Nausea and vomiting
  • Swelling airways, which can block breathing

Types of allergens causing Allergic Rhinitis (hay fever)

The most common allergens are pollens and dust mites. Allergic rhinitis, or hay fever, is the allergic response to pollen. It causes inflammation and swelling of the lining of the nose, as well as the protective tissue of the eyes (conjunctiva). Symptoms include sneezing, congestion and itchy, watery eyes. Treatment options include over-the-counter and prescription oral and topical medications. These medications include antihistamines, intranasal cromolyn, intranasal steroids, oral antileukotrienes, oral decongestants, and others. Among the most effective strategies to reduce allergic rhinitis symptoms is avoidance.

Avoiding pollen exposure by staying indoors when pollen counts are high, closing windows and using air conditioning will help reduce symptoms. Avoidance of indoor allergens such as dust mites and mold spores entails measures to reduce indoor humidity. Dust mite exposure can also be reduced by mattress/box spring and pillow encasement, and washing all bedding in hot cycle frequently. Avoiding pets is a challenge for many patients, but can be a very important factor in improving symptoms of allergic rhinitis and/or asthma. When avoidance measures combined with regular use of medications is not effective, not feasible or not desirable, immunotherapy (allergy shots) may be considered.


Pollens are microscopic particles released in to the air by trees, grasses and weeds. When these particles are inspired, people who have inherited the potential to make allergic responses in their immune system may become sensitized. When they are subsequently re-exposed to the same pollen, they may experience symptoms of allergic rhinitis.

Dust mites

Dust mites are microscopic insects that live in dust and in the fibers of household objects not frequently laundered, such as pillows, mattresses, carpet and upholstery. Dust mites require warm, humid areas. The symptoms of dust mite allergy are similar to those of pollen allergy, and also can produce symptoms of asthma such as wheezing and coughing. To help avoid dust mite allergens, try using dust mite covers (air-tight plastic/polyurethane covers) over pillows, mattresses and box springs. Also, remove carpeting or vacuum frequently using a vacuum cleaner with high efficiency filters. Treatment frequently also includes medications and/or allergen immunotherapy (allergy shots).


Molds are parasitic, microscopic fungi with spores that are also released in the air — like pollen. Mold can be found in damp areas, such as the basement or bathroom, as well as in the outdoor environment in grass, leaf piles, hay, mulch or under mushrooms. Mold spores peak during hot, humid weather.

Animal dander

The proteins secreted by sweat glands in an animal’s skin, which are shed in dander, and the proteins present in an animal’s saliva cause allergic reactions in some people. Treatment involves avoiding exposure as much as possible.

How are Allergy (Allergies) diagnosed?

If you experience allergic symptoms that last longer than a week or two and tend to recur, especially if they interfere with desired activities (e.g., exercising outdoors, work, school, a good night’s sleep), you may benefit from evaluation and management by a board-certified Allergy/Immunology physician. Allergy skin testing can be used to identify the allergens that are causing your symptoms. The test is performed by pricking your skin with an extract of an allergen and then evaluating the skin’s reaction. If a skin test cannot be performed, a radioallergosorbent (blood) test (RAST) may be taken.

The RAST evaluates allergy antibodies in the bloodstream produced by the immune system. Elevated levels of these antibodies can diagnose particular allergies, but this test is less sensitive than skin testing and for this reason is not preferred.

Treating Allergy (Allergies)

Medication for Allergy (Allergies)

Medication can't cure your allergy, but can be used to treat the common symptoms of an allergy, such as a runny nose, itchy mouth and sneezing. Most treatments are available over the counter but always ask your pharmacist or GP for advice before starting to take any new medication.


Antihistamines treat allergies by blocking the action of the chemical histamine, which the body releases when it thinks it is under attack from an allergen. Antihistamines can be taken in tablet, cream or liquid form, or as eye drops or nasal sprays.

Nasal sprays can be used to reduce swelling and irritation in your nose, and eye drops will help to relieve sore, itchy eyes. Some sprays and drops are only suitable for adults, so always ask your GP or pharmacist for advice before buying treatments for yourself or your children.


Decongestants help to relieve a blocked nose, which is often caused by hay fever, a dust allergy or a pet allergy. Decongestants can be taken as tablets, capsules, nasal sprays or liquids. They should not be used long-term.

Leukotriene receptor antagonists

Leukotriene receptor antagonists are tablets that block the effects of leukotrienes, which are chemicals released during an allergic reaction that cause inflammation (swelling) of your airways. They are used to treat asthma when other treatments have failed, and as a supplement to steroid treatment.

Steroid sprays

Corticosteroid sprays designed to act on the nasal lining and airways are effective in suppressing inflammation, particularly nasal congestion. Absorption into the body is minimal, so adverse side effects are avoided.

Hyposensitisation (immunotherapy)

Another form of treatment for allergies is hyposensitisation, also known as immunotherapy. 

Hyposensitisation works by gradually introducing more and more of the allergen into your body to make it less sensitive to it.

The allergens are usually given as injections under the skin of your upper arm. In the initial stages of treatment you will be given injections at intervals of a week or less, while allergen doses are gradually increased. When you reach the "maintenance dose", a dose that is effective in reducing your normal allergic reaction, you will need to continue to have injections of this dose every few weeks for at least two years.

Hyposensitisation is normally only recommended for the treatment of severe allergies (such as hay fever and pet allergies) that have not responded to other treatments, and for specific allergies such as bee and wasp stings.

This type of treatment must only be carried out under the close supervision of a doctor in a hospital, because there is a risk that it may cause a serious allergic reaction.

Treating anaphylaxis

If you have anaphylactic shock, you will need emergency treatment with an injection of adrenaline into the muscle.

If you have an allergy that could cause anaphylactic shock, or if you have had a severe allergic reaction in the past, you will be given an auto-injection kit of adrenaline. This is an easy-to-use syringe that you should carry with you at all times.

You might also want to consider wearing a medical information bracelet or another form of identification that carries information about your condition.

If you suspect that you or someone you know is having anaphylactic shock, ask for an ambulance.

Prevention and Home Remedies for Allergy (Allergies)

The best way to prevent an allergic reaction is to avoid the allergen that causes it.

This is not always easy. Allergens such as house dust mites or fungal spores can be hard to spot and can breed in even the cleanest house.

It can also be hard to avoid pets, particularly if they belong to friends and family, and many food allergies are triggered because people do not realise they are eating food to which they are allergic.

House dust mites

One of the biggest causes of allergies are dust mites. Dust mites are microscopic insects that breed in household dust. Below are ways that you can limit the amount of mites in your house.

  • Choose wood or hard vinyl floor coverings instead of a carpet.
  • Fit roller blinds that can be easily wiped clean.
  • Clean cushions, soft toys, curtains and upholstered furniture regularly, either by washing (at high temperature) or vacuuming.
  • Use synthetic pillows and acrylic duvets instead of woollen blankets or feather bedding.
  • Use a vacuum cleaner fitted with a HEPA (high efficiency particulate air) filter, because it can remove more dust than ordinary vacuum cleaners.
  • Wipe surfaces with a damp, clean cloth, as dry dusting can spread the allergens further.
Concentrate your efforts at controlling dust mites in the areas of your home where you spend the most time, such as the bedroom and living room.


It's not the pet fur that causes an allergic reaction, it's exposure to flakes of their dead skin, saliva and dried urine.

If you can't permanently remove a pet from the house, you may find the following tips useful.

  • Keep pets outside as much as possible, or limit them to one room, preferably one without carpet.
  • Don't allow pets in bedrooms.
  • Wash pets at least once a fortnight.
  • Groom dogs regularly outside.
  • Wash all bedding and soft furnishings on which a pet has lain (ideally at 60C).
If you are visiting a friend or relative with a pet, ask them not to dust or vacuum on the day you are visiting, as this will stir up the allergens into the air. Taking an antihistamine medicine one hour before entering a pet-inhabited house can help to reduce symptoms.

Mould spores

Moulds can grow on any decaying matter, both in and outside the house. The moulds themselves aren't allergens but the spores they release are. Spores are released when there is a sudden rise in temperature in a moist environment, such as when central heating is turned on in a damp house, or wet clothes are dried next to a fireplace.

Here are some ways that you can prevent mould spores:
  • Keep your home dry and well ventilated.
  • When showering or cooking, keep internal doors closed to prevent damp air from spreading through the house and use extractor fans.
  • Do not dry clothes indoors, store clothes in damp cupboards or pack clothes too tightly in wardrobes.
  • Deal with any damp and condensation in your home.

Food allergies

By law, food manufacturers must clearly label any foods that contain something that is known to cause an allergic reaction, such as celery, cereals, crustaceans, eggs, fish, milk, mustard, nuts, sesame seeds, soybeans and the preservatives sulphur dioxide and sulphites. By carefully checking the label for the list of ingredients, you should be able to avoid an allergic reaction.

Many people experience an allergic reaction while eating out at a restaurant. You can avoid this by:
  • not relying on the menu description alone (remember, many sauces or dressings could contain allergens)
  • communicating clearly with the waiting staff and asking for their advice
  • avoiding places where there is a chance that different types of food could come into contact with each other, such as buffets or bakeries
Remember, simple dishes are less likely to contain "hidden" ingredients.

Pollen allergies

Pollen allergies, more commonly known as hay fever, are caused when plants (trees and grasses) release pollen particles into the air. Different plants pollinate at different times of the year, so the months that you get hay fever will depend on what sort of pollen(s) you are allergic to. Typically, people are affected during spring (trees) and summer (grasses).

To avoid exposure to pollen you can:
  • Check weather reports for the pollen count and stay indoors when it is high.
  • Avoid drying clothes and bedding outside when the pollen count is high.
  • Wear wraparound sunglasses to protect your eyes from pollen.
  • Keep doors and windows shut during mid-morning and early evening, when there is most pollen in the air.
  • Shower, wash your hair and change your clothes after being outside.
  • Avoid grassy areas, such as parks and fields.
  • Get someone else to cut the grass for you if you have a lawn.

Severe allergies

If you have ever had a severe allergic reaction (anaphylaxis), make sure you carry two EpiPens or Anapens with you everywhere you go.

Wear a MedicAlert or Medi-Tag medallion or bracelet so that people are aware of your allergy in an emergency, and consider telling your teachers, work colleagues and friends so they can give you your adrenaline injection in an emergency while waiting for an ambulance. Following this advice could save your life.