Why do I have allergies

Allergies occur when your immune system reacts to specific proteins in substances foreign to it such as pollen, animal fur, insect venom, food or medication. These reactions do not occur in most people as these substances are usually harmless and in the case of food, vital to our survival.

Our immune systems produce substances known as antibodies that protect us against various infections. When you have allergies, your immune system makes antibodies that identify a particular allergen as harmful, even though it isn’t. When you come into contact with the allergen, your immune system’s reaction can inflame your skin, nose, eyes, airways or digestive system.

The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis, a potentially life-threatening emergency. Allergies of the skin and respiratory system are more common than those caused by food or medications. While most allergies can’t be cured, treatments can help relieve your allergy symptoms.


An allergy starts when your immune system mistakes a normally harmless substance for a dangerous invader. The immune system then produces antibodies that remain on the alert for that particular allergen. When you’re exposed to the allergen again, these antibodies can release a number of immune system chemicals, such as histamine, that cause allergy symptoms.

Common allergy triggers include:

—Airborne allergens, such as pollen, animal dander, dust mites and mould —Certain foods, particularly peanuts, tree nuts, wheat, soy, fish, shellfish, eggs and milk —Insect stings, such as from a bee or wasp —Medications, particularly penicillin or penicillin-based antibiotics —Latex or other substances you touch, which can cause allergic skin reactions.

Risk factors

You might be more likely to develop an allergy if you:

—Already have another allergic condition. —Have a family member with an allergic condition. —Delay introduction of proteins in your infants diet. —Nowadays, allergies are occurring in people who have no previous family history. This is due to the effect of urbanisation in our immune system.


Having an allergy increases your risk of certain other medical problems, including:

—Malnutrition: elimination of vital proteins especially in a child’s diet can be very harmful especially if unsupervised by a doctor or nutritionist qualified in allergies. —Sinusitis and infections of the ears or lungs. Your risk of getting these conditions is higher if you have hay fever or asthma. —Skin infections are more common in patients with eczema —Anaphylaxis is more likely in patients who have asthma especially when asthma is uncontrolled. —Poor self-esteem is more common in patients with eczema or recurrent facial swelling as this can cause disfigurement. Children with asthma or food allergies feel isolated as they do not engage in social activities such as sports, school trips or parties.

Symptoms associated with allergic reactions

—Allergy symptoms depend on the substance involved and can affect your eyes, nose, sinuses, chest, skin, and digestive system. Allergic reactions can range from mild to severe. In some severe cases, allergies can trigger a life-threatening reaction known as anaphylaxis.

Allergic rhinitis can cause:

—Sneezing, itching of the nose, eyes or roof of the mouth, runny, stuffy nose, watery, red or swollen eyes (conjunctivitis)

Asthma can cause:

—Wheezing, recurrent cough, chest tightness and difficulty exercising or playing.

Food allergy can cause:

—Hives, tingling in the mouth, swelling the face, hands and feet, sudden onset of diarrhoea or swelling and anaphylaxis.

Insect sting allergies can cause:

—A large area of swelling (edema) at the sting site, itching or hives all over the body and anaphylaxis.

Drug allergy can cause:

-Hives, rash, body swelling, wheezing anaphylaxis and eczema

Eczema: This condition occurs when the proteins that join skin cells are either absent or not working properly. The main function of the skin is to protect us from harmful substances that can cause infection.

When your skin barrier is deficient the immune system is activated at the breach to help protect you. When the normal harmless substances are introduced to the activated immune system at the breach, antibodies can be formed to specific proteins in those allergens.

In this way, eczema can be worsened by different allergens (proteins) and irritants (chemicals in soaps and moisturisers or mechanical trauma caused by scratching).

Symptoms of eczema include:

—Dry skin, itchy skin, redness and thickened areas of skin.

Remember: Eczema is not a food allergy. It is a skin barrier defect that can be worsened by different irritants and proteins in various substances including food.

Anaphylaxis: Some types of allergies, including allergies to foods, insect stings or medications can trigger a severe reaction known as anaphylaxis. This reaction usually occurs within minutes to two hours after exposure and is usually very dramatic. Allergic reactions became a life-threatening medical emergency when your airway, chest or blood pressure is affected.

Signs and symptoms of anaphylaxis include all of those mentioned above accompanied by ANY of the following;

-Cough, dizziness, wheezing, chest tightness, hoarseness of voice, shortness of breath, loss of consciousness and feeling of impending doom (something really bad is about to happen)

When to see a doctor

Immediate reactions occurring within two hours must be evaluated at a hospital. Those who have epipen or emerade must use it as advised by the doctor as soon as anaphylaxis develops.

You also need to see a doctor when your symptoms are recurrent, troublesome and non-responsive to medications.


Preventing allergic reactions depends on the type of allergy you have. General measures include the following:

—Avoid known triggers. Even if you’re treating your allergy symptoms, try to avoid triggers. If you’re allergic to pollen, stay inside with windows and doors closed when pollen is high. If you are allergic to pets keep them out of the house. —Keep a diary. When trying to identify what causes or worsens allergic symptoms, track activities and what you eat, when symptoms occur and what seems to help. This may help you and your doctor identify triggers for allergies that are not caused by antibodies. —Wear a medical alert bracelet. If you’ve had a severe allergic reaction, a medical alert bracelet (or necklace) lets others know that you have a serious allergy in case you have a reaction and you’re unable to communicate. An anaphylaxis action plan can guide a bystander on how to use the injectable adrenaline. —Use your controller medications regularly. These medications prevent immune cells from producing chemicals responsible for the symptoms.

Dr Karagu is an allergy specialist at Aga Khan University Hospital, Nairobi

This is especially important for those with asthma, eye and nasal allergies. Regular and aggressive moisturising in eczema maintains your skin barrier and decreases your steroid requirement.

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