Allergies occur when the immune system overreacts to a substance that is typically harmless to most people. These substances are called allergens, and they can be found in a variety of sources, such as pollen, mold, animal dander, and certain foods. When an allergic individual is exposed to an allergen, their immune system mistakes it for a harmful substance and mounts an immune response. This response can lead to a range of symptoms, including sneezing, itching, and difficulty breathing.
There are many factors that can increase the risk of developing allergies, including a family history of allergies, exposure to allergens during early childhood, and living in a polluted environment. Some people are more sensitive to allergens than others, and it is not fully understood why this is the case. However, research suggests that genetics, environment, and other factors may all play a role.
Common allergy triggers include:
- Airborne allergens, such as pollen, animal dander, dust mites and mold
- 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:
- Have a family history of asthma or allergies, such as hay fever, hives or eczema
- Are a child
- Have asthma or another allergic condition
Complications
Having an allergy increases your risk of certain other medical problems, including:
- Anaphylaxis. If you have severe allergies, you’re at increased risk of this serious allergy-induced reaction. Foods, medications and insect stings are the most common triggers of anaphylaxis.
- Asthma. If you have an allergy, you’re more likely to have asthma — an immune system reaction that affects the airways and breathing. In many cases, asthma is triggered by exposure to an allergen in the environment (allergy-induced asthma).
- Sinusitis and infections of the ears or lungs. Your risk of getting these conditions is higher if you have hay fever or asthma.