Assertion : Mast cells in the human body release excessive amounts of inflammatory chemicals which cause allergic reactions. Reason : Allergens in the environment on reaching human body stimulate mast cells in certain individuals.

Step-by-step solution

Mast cells act on body's defense mechanism. When some allergens like different pollutants, smog, smoke, pollen grains etc. come in contact with mast cells, they stimulate the mast cells. The allergic reaction is triggered by cross linking of IgE molecules on the surface of mast cells by allergen and ultimately mast cells release excessive amounts of inflammatory chemicals which cause allergic reactions.