The reasons why hamsters can't open their eyes:

1. Foreign body irritation may be caused by foreign bodies entering the hamster's eyes. The owner can use a clean cotton swab dipped in eye drops to wipe away the secretions from the hamster's eyes.

2. If the hamster gets internal heat, it may be that the hamster has eaten too much food containing high fat content, which may lead to eye inflammation caused by internal heat. The owner can use anti-inflammatory eye ointments and eye drops to instill into its eyes or feed it anti-inflammatory drugs to treat it.

3. Bacterial infection may be due to excessive dust in the environment where the hamster lives, or the environment is not clean, causing the hamster's eyes to become infected. The owner can send it to the pet doctor as soon as possible.