Yes essential oils can be harmful to your health if you abuse the essential oils or do not use the essential oils correctly.
Or if you use the essential oils too much then the essential oils may be harmful.
However when used in the correct ways and not abused or not overused the essential oils are healthy and safe to use.
You should never consume or ingest any essential oils because when ingested or consumed the essential oils can be harmful and are poison.
You can be poisoned when you consume or ingest essential oils.
So as long as you never ingest or consume any essential oils you should be safe using essential oils.