Can wearing ear bud headphones 24/7, literally, cause damage? if so how and what symptoms could occur?

Yes,: especially if the volume is too high. It can cause irreversible sensorineural deafness or hearing impairment. Some estimate that over 5% of current young adults and teenagers may have hearing impairment from such use.

Yes: In all seriousness, the principal damage would be psychosocial from stunted interpersonal relationships. That's what would most concern me. Aside from that, loud volume can cause permanent hearing loss. I suppose dermatitis might occur from accumulation of oils and bacteria in the foam.

Risk of hearing loss: Damage to hearing by high volumes is determined by duration, even at reasonable volumes can damage delicate hair cells in the inner ear that transmit sound impulses to the brain. 1 in 5 teens has some form of hearing loss - 30% higher than in the 80s/90s - experts believe due, in part, to the increased use of headphones. https://www.nlm.nih.gov/medlineplus/ency/patientinstructions/000495.htm