Colds and flu are viral illnesses that infect your upper respiratory tract, causing symptoms such as chest congestion, runny nose, watery eyes and cough. Influenza, more commonly known as the flu, can also cause fever, nausea and vomiting. Although there is no cure for either of these illnesses, certain herbal teas may help relieve the symptoms of these illnesses. Check with your physician before using any herbal tea to treat cold or flu symptoms.