What is allergic reaction?

In day to day life we come across conditions where we hear that someone got an allergic reaction. Many of you may have experienced the allergic reaction on first hand as self experience or with your family members.

Today let us discuss allergic reactions and some interesting facts about them. E will cover some background information about it then we will expand further to make it easy to understand for you.

What is immunity?

You and I are literally surrounded from each direction by our environment. This environment also has those harmful infectious disease agents around you. We are under threat of attack from these infectious agents each moment. 

They can come through air, water, food, soil, touch and what not. So mother nature has enabled us to fight those infectious agents. You have literally an army of fighters in your body. This army which fights these infectious agents is called immunity.

So basically your immunity protects you from infectious agents, so you are alive. Sometimes these infectious agents can overpower your immunity and you can feel the disease symptoms. Sorry for using mild words literally you can suffer the disease if your immunity is not able to contain those infections.

Immunity is of 2 types. One is innate immunity and other is adaptive immunity.

Innate immunity is a power you have got from nature. It is inbuilt immunity. This immunity is present at birth with you. It is effective in protecting you from some diseases.

Adaptive immunity is what you develop in the process of life. Innate immunity is insufficient to fight some infections. Like your macbook needs updates, your immunity too needs updates to fight the new infectious agents. This immunity is developed when you are exposed to the infections. It helps you to protect yourself when you get infected with the same agents next time.

But the drawback of developing adaptive immunity after getting exposed to infection is you may have to suffer from a disease in the process. The disease may cost some lives in the process. So to avoid this suffering and loss, we have vaccines.

In further sections we will see how these vaccines help you develop your immunity.

What is an allergic reaction?

In the previous paragraph we have discussed immunity. This immunity plays a major role in allergic reaction.

Our immunity detects the foreign antigen as not our own and attacks it if it feels that the antigen is harmful for us. Till it attacks it in a way it should we won’t feel any effects on our own.

But when this action is excessively strong and our body feels the harm of this action we call it an allergic reaction.

When immunity works it fights the offender by secreting some chemicals like histamine. These chemicals have their role in normal functioning of the immunity.

When these chemicals are secreted in excess, they show their bad effects rather than being helpful for us.

Allergic reaction can be as mild as a running nose to as severe as a life threatening anaphylaxis reaction in which death can occur.

What is allergen?

Allergen is anything that induces allergic symptoms stated above. You may come in contact with allergen from food, air particles or water or your surrounding environment.

After coming in contact with allergen you suffer the allergic symptoms. Allergen induces your own body cells to secrete normal chemicals in abnormal amounts that makes you suffer to face all these symptoms.

Literally anything under the sun, including the sun can cause you allergic manifestations. 

What are the common allergens?

As we discussed earlier allergens can be anything that induces allergy or allergic reaction in an individual. Though anything can induce allergic reaction, here are some common items that induce allergies very commonly in many people:

  • Pollen grains.
  • Insect bites.
  • Dust mites.
  • Coloring agents and preservatives in food.
  • Peanuts and groundnuts.
  • Cow milk.
  • Egg proteins.
  • Metal ornaments and jewelries containing nickel.
  • Congress gass.
  • Cat and dogs hair.
  • Other pet animals’ hair.
  • Exposure to cold.
  • Cold food.
  • Wheat and soy proteins.
  • Some fruits like apples and bananas.
  • Strong scents and smells.
  • Medicines like penicillins.

The list is extensive but above all are the objects that are common in inducing allergies and allergic reactions. Other agents induce allergies less commonly.

What are symptoms of allergic reactions?

If you already are allergic to anything you may have already experienced the symptoms of allergic reactions.

The symptoms of allergic reactions are of wide variety and vary from mild to moderate symptoms from episode to episode and from person to person.

Mild allergic symptoms are: 

  • Stuffy nose, running nose, itching nose and pharynx.
  • Itching and urticaria and redness of the skin.
  • Itching of eyes and watering of eyes.
  • Vomiting and loose motions.
  • Swelling of eyelids and limbs.

Severe symptoms of allergic reaction that can be life threatening are:

  • Difficulty in breathing.
  • Severe abdominal cramps.
  • Dizziness and fainting.
  • Low blood pressure.
  • Swelling of lips and tongue and larynx obstructing the breathing.
  • Increased heart rate or decreased heart rate.
  • Death.

Severe allergic reaction is called anaphylactic reaction can occur within minutes of exposure to allergen and can cause death in some minutes.

What is anaphylactic reaction?

Anaphylactic reaction is the most severe form of allergic reaction which occurs within minutes of exposure to allergen and can lead to death in a few minutes.

In anaphylactic reaction there is difficulty in breathing and lowering of blood pressure. Fainting, dizziness and unconsciousness can occur in a few minutes. If not treated promptly it can cause death in the patients.

How to manage allergic reaction?

Allergic reaction is managed depending on severity of symptoms. For mild symptoms oral treatment can be given for severe reactions like anaphylaxis injectable medicines with life supporting treatment is needed.

Following are the medicines that can be used for stable patients which can take medicines orally.

Mild allergic reactions

Acute management is useful for reducing the current symptoms in those suffering from allergic reaction. Current symptoms may range from mild to severe.

When the current symptoms are affecting day to day function of the person they should be treated.  Following are the treatment options available in this condition


Antihistamines are antiallergic in nature. They reduce the secretion of histamines by the histamine secreting cells and histamine is the main allergy inducing agent that causes symptoms of the allergy.

Antihistamines show effects in hours depending on which drug was used. Antihistamines are classified according to the time they were invented. Older generation antihistamines cause more sedation and newer ones are comparatively less sedating.

Hydroxyzine and promethazine and chlorpheniramine are amongst older antihistamines.

Loratadine, fexofenadine, cetirizine and levocetirizine and bilastine are among newer ones.

Antihistamines can be used orally or locally as a nasal spray like azelastine nasal spray. 

These agents though are many available OTC should be used cautiously as they may cause addictions if used in the wrong way and also dangerous if given in overdose.

Some of them like hydroxyzine and fexofenadine may cause arrhythmia in some patients.

The anticholinergic effects which they have helps 

  • Dry up the nasal and pharyngeal mucosa 
  • Reduce the stuffiness of the nose 
  • Itching sensation

Sedating antihistamines is a drug choice in children where sleep disturbance is there along with nasal secretion and stuffiness symptoms.

Adults who need to drive or work at places where attention is needed should be given newer antihistamines which cause less sedation. You should keep in mind though newer antihistamines too may cause decreased alertness with other medications.


This is the drug that causes the constriction of blood vessels in the nasal mucosa. Due to this constriction of the blood vessels in nasal mucosa the blood flow to nasal mucosa is decreased.

The secretions on nasal mucosa are decreased and dried up. It gives relief from symptoms of nasal secretions and stuffiness.

This is given usually orally in combination with antihistamines. Many OTC cough cold medications contain phenylephrine as a content. 

This should be given in proper dosages and with advice of the doctor as overdoses are dangerous and it may cause high blood pressure.

This drug is not safe to use in pregnant ladies and infants and small children. It can be dangerous in older adults too.

Oral steroids

Steroids are antiallergic and antiinflammatory effects. They do reduce the symptoms of allergy in allergic reaction.

They are useful orally or by injection or by nasal spray. Steroids act in a few hours and are safe when doctor prescribes it.

Some of the examples are prednisolone for oral use and dexamethasone for injection and fluticasone and mometasone as nasal spray.

Used for prolonged periods these may cause hypertension, diabetes and cataract and kidney failure. Do not use them without advice of a doctor.

Used in the wrong manner they may cause severe immunosuppression and that can be dangerous to the person. In the long run these can weaken your bone altering your calcium metabolism.

Antiinflammatory drugs

Antiinflammatory drugs reduce the pain and inflammation. There may be presence of inflammation in allergic reaction.

Antiinflammatory drugs help to reduce those symptoms. They also reduce the fever if present. 

Some of the examples are paracetamol and ibuprofen. Many OTC cough cold medications contain combinations of antihistamines and phenylephrine plus paracetamol. They may have added caffeine to reduce the side effect of sedation.

Nasal sprays of oxymetazoline

Oxymetazoline and xylometazoline give immediate relief of symptoms when sprayed into the nose. They act by constricting the blood vessels in the nasal mucosa.

Oxymetazoline gives symptomatic relief from the symptoms of nasal secretion and nasal stuffiness. They show their effect within a few seconds.

These medicines though many times available as OTC. Do not use them for more than 5-7 days as they have habit forming potential.

They do cause sleepiness and feeling fatigue. They may give you a stingy sensation in your nose.

Those with hypertension and older adults should not use these medicines as they are not safe in this age group. 

Additionally tavoid these drugs for those below 12 years of age as they are not safe to use in this age group.

Severe allergic reaction

For severe allergic reactions that can be life threatening the management should be done promptly. The emergency drugs given prompt can save the life of the patient. Following are some measures to do when someone gets a severe allergic reaction.

Leg high position

Patients with severe allergic anaphylactic reactions suffer low Blood pressure due to dilation of vessels which leads to failure of blood circulation. 

Patient is made to lie supine and legs at a higher level than head. This helps for blood to flow to the heart so that the heart pumps blood effectively and can circulate blood.

Epinephrine injection

Epinephrine injection is the only drug that can reverse anaphylactic or severe allergic reaction. It can be intramuscular. Auto Injector epipen are useful for the purpose.

Epinephrine is the strongest antihistamine drug that can reverse the allergic symptoms in seconds. It also causes vasoconstriction and restoring blood pressure and circulation to the normal level.

Epinephrine reduces the edema of the larynx and respiratory tract so that patients can breath and can survive.

Injectable steroids

Injectable steroids like dexamethasone or hydrocortisone can relive the patients from allergic reaction symptoms. Practitioners use them as they are strong anti allergies and they show their effects in a few minutes.

Injectable antihistamine drugs

Injectable antihistamine drugs are the other class of drugs that are strongly anti allergic and they can reverse the symptoms of allergic reaction in a few minutes.

How to prevent allergic reaction?

How to prevent allergic reaction is the question that arises on everyone’s mind. Following are the ways to prevent allergic reaction or the harm caused by that:

Avoiding allergens

Avoiding allergens is the best strategy to prevent allergic reaction. Especially if you know you are allergic to something you should avoid that allergen.


Those who have a tendency to get severe allergy should keep Epipen with them. Epipen contains the medicine Epinephrine which is a life saving drug in case of severe allergy. With Epipen which has auto injector the epinephrine can be injected automatically with minimal help.


Those who have severe allergy to something should carry an Id Card stating their condition and instructions to be followed if they get an allergic reaction.

Food labelling

Many people may be allergic to food ingredients like peanuts and soy protein. They may get a severe allergic reaction after consuming such food. The food should be labeled with its contents so that you can avoid the food you are allergic to.


Everytime you visit your doctor or chemist, you should tell them if you are allergic to any medicine so that they can help you to avoid that medicine.


Mearing masks may help you from exposure to dust and pollen where you are likely to get exposed to them.


Wearing clothes that cover the entire body when you are likely to come in contact with grass may protect you from contact dermatitis.


If you have nickel or metal like gold and silver allergy you should avoid wearing the jewelry made up of them and find some alternative if at all needed. Defer the ear or skin piercing in such conditions.

<span class="has-inline-color has-luminous-vivid-orange-color">Dr Yatin Bhole MBBS DCh DNB</span>
Dr Yatin Bhole MBBS DCh DNB

This article was written by Dr Yatin Bhole who is practicing Pediatrician at Bhole Children Clinic, Ravet. This post is for general information and before applying it on yourself, you should meet your doctor or meet us in person.

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