When wearing contacts, one eye may become painful while the other is normal, which may be due to the following reasons: 1. Conjunctivitis. If you wear contacts when you have conjunctivitis, you may experience eye congestion, foreign body sensation, and grinding pain, so you should immediately remove your contacts and add levofloxacin drops four times a day, one drop at a time. 2. Corneal epithelial damage. When wearing contacts, the wrong technique or excessive force can cause damage to the corneal epithelium, resulting in pain, foreign body sensation, photophobia, and tearing. 3. Damage to the pupil. When wearing contacts, excessive force can also lead to damage to the corners of the contacts, resulting in painful wear and foreign body sensation. Therefore, if you experience eye pain after wearing contacts, you should immediately remove them and look for the cause of the pain, and treat it accordingly.