Reactine Extra Strength Allergy Relief Tablets relieves indoor and outdoor allergy symptoms. Indoor allergens, including mold, dust, and pet dander can cause allergy symptoms at home and at work. Since indoor allergies can be triggered any time of year, can often be easily confused with a cold. Understanding and recognizing the symptoms is half the battle. Allergy symptoms kick in when your immune system overreacts to substances called allergens. Your body releases many chemicals, one of which is called histamine. Histamine is the most abundantly released chemical and is responsible for causing most of your symptoms. Antihistamines are your first line of defense for allergy symptom relief.