Ulcerative colitis — long-term swelling and sores in the large intestine — often shifts between two phases. During remission, the disease is quiet and symptoms ease. During a flare, symptoms come back or get worse. The most common flare symptoms are belly pain and blood or pus in diarrhea. Other symptoms can include severe tiredness, weight loss, loss of appetite, and bleeding from the rectum. Some people also notice joint pain or sores on the skin. About half of people with UC have mild symptoms overall. Let your care team know right away if your symptoms return or worsen.