When you have a cold, allergies, or sinus trouble, the membranes in your nose, sinuses, and chest can swell and block the flow of air. This makes you feel stuffy or congested. A decongestant is a kind of medicine that helps shrink the blood vessels in these membranes, lowering the swelling and helping you breathe easier. Decongestants are found in many kinds of cold, flu, sinus, and allergy medicines, but not all. To find out if the medicine you want to take has a decongestant in it, look at the drug facts label on the package. This label will show the names of all the active ingredients in the medicine and their purpose. Even if you don’t have high blood pressure or a heart problem, it’s a good idea to talk to your doctor or pharmacist before you take a new kind of medicine.