Bloodshot eyes are not a sign of serious illness, but are more likely to be caused by conjunctivitis, keratitis, iridocyclitis and other diseases. 1. Conjunctivitis: the cause of the disease is more, may be due to infection, immune lesions and other conditions, and also with the body’s immunity to decline, the underlying disease, wearing contact lenses and other factors. Patients often have symptoms such as red eyes, dryness, excessive secretions, tearing, and some patients may also have bloodshot eyes. Some patients may also have a foreign body sensation, fear of light and other phenomena. 2. Keratitis: usually due to corneal defense ability is weakened, by external pathogens or their own disease, and also with the cornea foreign body, long-term in the warm and humid environment and other factors. Patients often appear eye pain, tearing, eyelid spasm and other symptoms, and can also be accompanied by conjunctival congestion, blurred vision, vision loss and so on. 3. Iridocyclitis: the cause of the disease is more complex, may be due to immune dysfunction, trauma, physical and chemical damage and other conditions, and also with bad mood, fatigue and other factors. Patients often have symptoms such as eye redness, eye pain, photophobia, etc., and may also have bloodshot eyes. Some patients may also have black spots or black shadows in front of their eyes. It is recommended to identify the cause of bloodshot eyes and take reasonable treatment measures.