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Allergies occur as a result of an immune response to a foreign substance that is usually not harmful and can be tolerated by the human body. The substances which trigger your immune system are called allergens, and the response triggered by them is known as an allergic reaction. An allergen can enter your system in various ways. Once your immune system identifies it, it begins a chain of reactions to remove that substance from the body. In the duration of this response, the affected person may suffer from mild to severe complications. 


Allergies can occur due to a number of different substances. Some individuals are genetically predisposed to certain allergens, while others may acquire them during their lifetime. An allergen can enter your system via four ways which include skin, ingestion, inhalation, and injection.

Skin allergies are a very common form in which the skin gets itchy or swollen as a reaction to an allergic substance. This can include certain topical medications, jewelry, latex gloves, poisonous plants, pet hairs, etc. You may also be allergic to certain cosmetic products and makeup.

Ingestion allergies can be caused as a reaction to particular food substances or oral medicines. Lactose intolerance and nut allergies are some of the most common forms of allergic reactions. Among medicines, penicillin allergy is common and should always be taken into consideration before taking an antibiotic.

Allergens that cause inhalational allergies enter your system through your nose or mouth. If the allergic reaction is severe, it can lead to airway obstruction and irregular breathing, which can be a life-threatening complication. Dust and pollen allergies are two of the most common inhalational allergies.

Injection allergies are usually caused after injection of a medicine or drug into your system. An allergic reaction occurring after a mosquito bite can also be considered an injection allergy because it pierces the skin to reach your blood circulation. 


There are many types of allergies, but on a broad scale, they can be of the following types:

  • Food allergy
  • Drug allergy
  • Pollen allergy
  • Latex allergy
  • Insect allergy
  • Pet allergy
  • Mold allergy

Risk Factors And Epidemiology

Allergies have a strong genetic factor linked with them. If you have a family history of an allergy such as peanut allergy or pollen allergy, there is a probability that you may also have that allergy. The response of your immune system will be determined by your genetic factors.

It is also possible to develop allergies during childhood. Because the immune system in a child continues to develop as they are exposed to the environment, any particular substance that is not harmful can trigger their immune response. Their immune system identifies that substance as an allergen, and therefore, this allergy is carried on for their lifetime. People or older adults with a weakened immune system are also at a higher risk of developing allergies.

According to research, an estimated 41% of adults in America have different forms of allergies, including food allergies, skin allergies, pet allergies, and other types. 

Signs and Symptoms

Signs and symptoms of an allergic reaction depend on the causative allergen and its mode of entrance. Allergic reactions that occur on the skin can present with itching, redness, swelling, rashes, or peeling of the skin. In most cases, a localized allergic reaction occurs on the site of skin where the allergen came in contact. Food allergies can present with a tingling or burning sensation in the lips and soft tissues of the mouth, hives, swelling of lips, tongue, etc. In severe cases, an anaphylactic reaction occurs, which can cause airway obstruction.

Inhalational allergies can present with coughing, sneezing, runny nose, itching of eyes or nose, watery eyes, and anaphylaxis. If an anaphylactic reaction occurs, immediate medical attention is required as it can obstruct the airway. Other allergies resulting from medications, mosquito bites, or insects can also present with similar skin and respiratory symptoms. 


The diagnosis of an allergy begins with obtaining a detailed history of your symptoms and the presence of a family history. History is crucial in determining the type and severity of an allergy. This is followed by a physical examination to notice any active signs of an allergy. If your doctor suspects that you’re allergic, they will recommend allergic testing. This is usually done in two ways. One way is skin testing, in which a patch of your skin on pricked with possible allergens, and your skin reaction is noticed. If your skin becomes itchy or inflamed, it is likely that you have an allergy. The other way is to diagnose an allergy through blood tests. Specific IgE blood testing is done to determine the number of antibodies to a certain allergen. 

Differential Diagnosis

Respiratory allergies can often be confused with other respiratory illnesses such as influenza, rhinitis, sinusitis, bronchitis, etc. Skin allergies can also resemble other skin diseases such as atopic dermatitis, fungal infection, etc. These conditions should be differentiated on the basis of history and diagnostic tests


The primary focus of treatment after you’ve been diagnosed with an allergy is to avoid that allergen. Whether it is caused by a nut, pollen, or any other cause, avoidance techniques are implied to reduce the occurrence of an allergic reaction. If you develop an immediate life-threatening allergic reaction, an emergency epinephrine shot is given to lessen the symptoms.

Medications are given according to your type of allergy. These may include antihistamines such as loratadine, cetirizine, nasal decongestants, inhalers, eye drops, topical ointments or creams, and other oral medications. Patients with severe allergies need to carry these medications and an EpiPen with them at all times. 


Allergies can be present for your whole life, from mild to moderate severity. In the majority of the cases, they can be managed well with the avoidance of allergens and medications. 



Prevention of an allergy can be done by tracking your immune response to certain substances. If you notice that you develop a severe reaction after eating something or applying a cosmetic product, note it down along with your symptoms to avoid it in the future. Wear a mask during periods of seasonal allergies or in places with dust or mold. Avoiding the trigger factor is the best way to reduce the occurrence of an allergic reaction.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on May 10, 2023. 



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