Mast cells are a type of white blood cell that play a crucial role in the immune system. They are primarily found in tissues throughout the body, especially in the skin, lungs, and digestive tract. These cells contain granules filled with chemicals, such as histamine, which are released during allergic reactions and inflammation. When activated, mast cells release their granules, leading to various physiological responses. This can include increased blood flow, swelling, and the recruitment of other immune cells to the site of infection or injury. While they are essential for defending the body, overactive mast cells can contribute to allergic conditions like asthma and hay fever.