Its FEMA who issue the designation GRAS generally regarded as safe and as you say only in respect of the use of oils typically in 0.01% dose for their aroma (what gives food and drink its flavour). The FDA only comment on one or two oils.
In fact with the exception of tea tree and yarrow most common oils are
used in food and drink but only in such low doses. Besides anything
else it only takes such low doses to register an aroma with the nose.
Higher doses and you spoil the flavour and risk sensitisation.
In the 1-4% range we are talking beauty products (creams 1% wash off
shampoo 4%). In the 5-10% dilution range for specific conditions we are
talking clinical aromatherapy use by or sanctioned by qualified MDs or
Nurses. Yes over the counter neat in gel capsules for a limited number
of oils for a limited number of conditions for a limited amount of time.
Ingestion of 'active' substances is not really what the holistic
approach is about as I understand it. Infection apart more important is
the trained observational and personal skills of the practitioner, the
psycho-therapeutic properties of the aroma and methods of application
like touch. We are talking about what MDs call the "worried well".
Anyone who is ill should see a doctor.