Red eyes after a cold can be caused by lack of sleep, conjunctivitis and other factors. 1. Lack of sleep: During a cold, symptoms such as nasal congestion, runny nose and coughing may cause lack of sleep, which can easily lead to red eyes. Usually after the eyes get enough rest, the symptoms of red eyes can be improved, no need to worry too much. 2. Conjunctivitis: If the cold is a viral cold, it is easy to cause viral conjunctivitis, resulting in redness of the eyes, which can be treated with topical acyclovir eye drops. In addition, if the cold secondary bacterial infection, can also be through the nasolacrimal duct secondary bacterial conjunctivitis, will also appear in the eye redness symptoms, can use levofloxacin eye drops. In addition to this, there are other diseases that can also cause symptoms of red eyes. If the symptoms do not improve or worsen, it is recommended to consult a doctor in a timely manner to clarify the cause of the disease and standardize the treatment under the guidance of the doctor, so as not to delay the condition.