Reflux is an extremely common problem, affecting an estimated 20 million Americans. It occurs when food and acid from the stomach back up into the esophagus, or food tube. The most common symptom is heartburn, but reflux can also show up as hoarseness (backed-up acid attacks the vocal cords), sinusitis (acid irritates tissues in the nose) and asthma (droplets of acid get inhaled into the lungs).