Below are authoritative books and scientific papers for your knowledge:
Differences In Immune Responses Induced By Oral and Rectal Immunizations
Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health
The Role of Gut, Vaginal and Urinary Microbiome in Urinary Tract Infections: From Bench to Bedside
Immunomodulatory Activities of Selected Essential Oils
The Effectiveness of Aromatherapy for Depressive Symptoms: A Systematic Review
Herbal beverages: Bioactive compounds and their role in disease risk reduction - A review
There is more to come...