Allergies occur when your immune system reacts to a foreign substance — such as pollen, bee venom or pet dander — or a food that doesn't cause a reaction in most people.
Your immune system produces substances known as antibodies. 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, sinuses, airways or digestive system.
Allergies are often seasonal, but can also be present year round. While they affect different people in different ways, the typical symptoms include:
- itchy and/or red eyes
- itchy palate
- itchy and runny nose
- sneezing and nasal congestion (allergic rhinitis)
- difficulty breathing
These symptoms may be accompanied by headache, sinusitis, or a rash. In some cases, these will be the only signs of the allergy.