Essential oils and chickens

Can I suggest caution in the use of essential oils especially on animals, in particular those who preen themselves.  Essential oils are potentiality poisonous.

The chemical components of some oils are carcinogenic , Tee Tree in particular is seen as safe along with Lavender however, if used inappropriately they will at best cause irritation and at worst poison.

Essential oils should never be ingested ergo using them on birds can be very dangerous.