That you are a licensed primary health care practitioner (D.C., D.O., M.D. or N.D.) or someone who has held licensure previously, and are in good standing. The N.D. must be from a fully accredited school from which graduates are eligible for licensure.
You should have held a license and practiced actively for a minimum of 3 years for the "experienced list".
For less experience use the "public contact list".
That your hygienic practice is not drug based.
Either that you have a Natural Hygiene certificate (e.g. from IAHP)
OR that you have basic knowledge about Natural Hygiene, and have read "Natural Hygiene - A Pristine Way of Life" by Herbert Shelton.
(How can you prove it? By emailing/writing a short book review/report about the book. And a short essay about what you think Natural Hygiene is and what your experience in it is.)
That you provide a link to naturalhygienesociety.org from your (eventual) website, in return to INHS link to your site.
Note: "Natural Hygiene - A Pristine Way of Life" by Herbert Shelton is available to read online at soilandhealth.org
Note: you can have other businesses as long as you keep them clearly separated from your hygienic practice.
Continuing education
What continuing Natural Hygiene (Nature Cure) theoretical education for experienced hygienic doctors is there? There are not many options today, the best is probably a quality theoretical hygienic course.
Communication with other experienced doctors is always very important. Since doctors who do not believe in "cures" and not use drugs are a small minority, it is essential to have a strong contact network. Become a INHS member and join the email discussion group.