Sensitization is a process in which an individual's immune system becomes increasingly responsive to a specific substance, known as an allergen. This heightened response can occur after repeated exposure to the allergen, leading to stronger reactions over time. Common allergens include pollen, pet dander, and certain foods. In psychology, sensitization refers to an increased reaction to a stimulus following a strong or noxious event. For example, after experiencing a loud noise, a person may become more sensitive to similar sounds. This can lead to heightened anxiety or stress responses in certain situations.