Reactine Extra Strength Allergy Relief Tablets provides allergy symptom relief for both indoor and outdoor allergy symptoms. Reactine Extra Strength lasts 24 hours, all day and night. Antihistamines are your first line of defense for allergy sympom relief. Antihistamines treat itchy and watery eyes, runny nose and sneezing, itchy nose and throat, and allergic skin itch (like hives) caused by seasonal and perennial allergies. Reactine contains 10-milligrams of Antihistamine Cetirizine Hydrochloride which provides fast, 24-hour symptom relief. 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. 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, they can often be easily confused with a cold. Outdoor pollen from the spring, summer, and fall can be present inside your home too. Speak to your doctor or pharmacist. To be sure this product is right for you, always read and follow the label.