During an allergic reaction, substances called …………………………….. are released by the mast cells.

Explanation

**Step-by-Step Solution:**

1. **Understanding Allergic Reactions**: An allergic reaction is an exaggerated response of the immune system to certain antigens, which are typically harmless substances like pollen, dust, or certain foods.

2. **Role of Mast Cells**: Mast cells are a type of white blood cell that play a crucial role in the immune response, particularly in allergic reactions. They are found in various tissues throughout the body.

3. **Substances Released**: During an allergic reaction, mast cells release specific substances that contribute to the symptoms of the allergy. The primary substances released are chemicals known as mediators.

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