The bible says evil spirits exist, but they're not physical like humans. Bro Eli said anything called spirit does not have flesh and bone like human. With all this, evil spirits cannot physically touch humans the way we touch ourselves. They base and do their things in the spirit world.
“Behold my hands and my feet, handle me, and see; for a spirit hath not flesh and bones as ye.” (Luke 24:39)
But we must know that evil spirits can still affect some people physically but in indirect ways. Evil Spirits can possess some people and they will begin to act violently, some may even fall sick. The person doesn't know itself, because the spirit has taken control over that person.
From the scripture, God is more powerful that all the evil spirits. In the bible Jesus commands demons out from humans, to show He is more than them. As a christians we have to put our trust in God, whoever that is prayerful and follows the ways of God cannot be affected by evil spirit.