Final answer:
A chemical that can trigger allergic reactions is known as a sensitizer, which can lead to an immune system response causing symptoms like sneezing and itching.
Step-by-step explanation:
Chemical Causing Allergic Reactions
A chemical that can cause allergic reactions is referred to as a sensitizer. An allergic reaction occurs when the immune system responds with an inflammatory reaction to a harmless antigen, termed an allergen. Allergens can be various substances ranging from pollen and food to insect stings and medications. Upon exposure to an allergen, a sensitized individual's immune system can rapidly react, often immediately, leading to symptoms such as sneezing, itching, and nasal congestion. Contrary to sensitizers, an irritant causes irritation to the skin and eyes without involving an immune response, and a corrosive substance can burn skin and eyes, while a mutagen is a substance that can cause mutations in DNA. Therefore, the correct answer to the question is 'A. Sensitizer'.