Conjunctivitis is an inflammation of the conjunctiva that is often caused by a viral infection, such as a common cold. It is common for both eyes to be affected during a cold. Using a clean damp towel to clean the affected area can help prevent the spread of infection. In most cases, the symptoms should improve within 5 to 7 days. If the symptoms persist for more than a week or worsen, it is important to seek medical advice from a doctor or optometrist.