1. Definition
Allergy is an exaggerated immune response to harmless substances (allergens), resulting in symptoms such as itching, swelling, or difficulty breathing.
2. Classification
- Respiratory allergies (e.g., pollen, dust mites)
- Food allergies (e.g., peanuts, shellfish)
- Skin allergies (e.g., contact dermatitis)
- Drug allergies (e.g., penicillin)
- Insect allergies (e.g., bee stings)
3. Cellular reaction
- Sensitization: Allergen exposure activates T cells, leading to IgE antibody production by B cells.
- Re-exposure: Allergens bind to IgE on mast cells or basophils, triggering histamine release, causing inflammation and allergic symptoms.
4. Symptoms
- Sneezing
- Runny or stuffy nose
- Itchy or watery eyes
- skin rash or hives
- swelling (especially of the face, lips, or throat)
- coughing or wheezing
- shortness of breath
- stomach problems (such as nausea, vomiting, diarrhea) with food allergies