In order to keep Essential oils affordable and available to everyone, distributors must talk about them in a highly generalized sense regarding the various ways essential oils can support your 12 body systems.
If you want to dive deeper, I recommend the following sources:
Google Scholar &-or PubMed 
Look up specific oils, or powerful constituents such as:
- Beta caryophyllene (e.g. Copaiba)
- Methyl salicylate, menthol, eugenol (e.g. Panaway TM)
- Alpha-pinene (e.g. Frankincense)
- D-limonene (e.g. Lemon)
If you’re looking for a book with a scientific approach
The Healing Intelligence of Essential Oils – Kurt Schnaubelt (Illuminating & affordable)
The Chemistry of Essential Oils Made Simple: David Stewart (deep dive, doctrinal)
Essential Oils Integrative Medical Guide: Gary D. Young (the book Gary wrote before he was censored by the FDA in what he could say about essential oils and their medicinal applications). I love this book but I will say that if you already have a good reference guide (such as the one I recommend below), there are many redundancies.
If you just want a good reference guide
My favorite is the Essential Oils Pocket Reference available from Life Science Publishing. You’ll receive this as a free gift when you sign up for your PSK using distributor #10672500. E-mail harriet@embodiedoiler.com with promo code “GUIDE” after you sign up.
This covers essential oils basics and safety and allows you to look up specific oils and blends, or find solutions based on diseases, ailments and imbalances.
If you prefer an app
Reference Guide for Essential Oils by Abundant Health (The app version of the book above)
EO Bar – recipes and education by Jennifer O’Sullivan
If you want to learn about essential oils from a lifestyle angle…
Lucy Libido Says…There’s an Oil for That. For using EO between the sheets & for 
hormonal balance
Renegade Beauty – Nadine Artemis. This book is not exclusively about essential oils, but offers a wealth of information about holistic health, specific oils, recipes and generating beauty from the inside out.
Holistic Dental Care – Nadine Artemis. Tips on how to use essential 
oils for oral hygeine.
Releasing Emotional Patterns with Essential Oils – Carolyn Mein. Oils for Emotional Support
Oil + Glass – The Essential Collective. Recipes
Gentle Babies Book – Debra Raybern. Oils for pregnancy, birth and children
If you want anecdotal data
Looking for resources about the business opportunity?
e-mail harriet@embodiedoiler.com and let me know you’re interested to learn how to get your oils paid for. I’ll forward you some of my favorite tools and resources.