Final answer:
Allergens are substances that cause allergies, such as pollen and plant oils. They can trigger allergic responses in sensitive individuals, leading to symptoms such as sneezing and an itchy rash.
Step-by-step explanation:
Allergies are caused by substances called allergens. Allergens, such as pollen, plant oils, and dander, can trigger an allergic response in sensitive individuals. Common allergens also include dust mites, mold, specific foods (such as peanuts or shellfish), insect stings, and certain medications (such as aspirin and penicillin). When these allergens are inhaled, ingested, or come into contact with the skin or eyes, they can cause symptoms such as sneezing, red itchy eyes, and an itchy rash, depending on the type of exposure and the severity of the immune system response.