Earplugs are generally safe. However, they do come with a few potential side effects, especially if you use them regularly. Over time, earplugs can push earwax back into your ear, causing a buildup. This can cause several problems, including temporary hearing loss and tinnitus.
Foam earplugs completely close off the ear and attenuate a reasonable amount of noise. They are not reusable and do not fit perfectly. There is no such thing as soundproof earplugs. Because the cranial bone also transmits vibrations to the eardrum, you will still hear louder noises.