Doug does not hold advanced research degrees or any medical qualifications but has been employed by CND, so I'll take what he says with a pinch of salt compared to my very experienced medically qualified Consultant any day.
That is nonsense in not having a senior research degree you can't do post doc work! I successfully defended my thesis last year and my external examiner only had an MEng. What sets him apart from the others is that he has extensive experience from other PhD's and numerous publications and citations from prestigious investigators from world renowned Universities equivalent to that of my Professor.
It is true that Douglas does not have an advanced senior degree such as an MPhil or a PhD degree (but I do) and he has a Masters degree in Chemistry, but note that Doug also stands as a witness in litigation cases and has authored a number of books and scientific publications and some are cited on google scholar. The importance of having such publications is that they are peer reviewed; where a body of newly created research is scrutinised by other researchers who are independent and verified if the facts and methodologies used are correct and if passed, it is accepted for publication. One thing I do notice is that there is a lack of conferences for nail technology.
One key skill you learn in doctoral training is the tone of language that the author uses and if there is any bias involved. I have one of his books; it is very toned down suited for the nail technician and I don't see that he actively promotes CND or any other products in any way - in fact he is neutral like science is intended to be. If I detected any bias, I would be the first to throw the book out of the window and consider it pseudo science.
https://scholar.google.co.uk/scholar?q=douglas+schoon&btnG=&hl=en&as_sdt=0,5
With regards to consultant physicians, they are humans and they make mistakes and their knowledge is dependent by research output since most of the knowledge creation is taken from by reputable researchers - Universities is an example of a knowledge creation institute.
I'll give you an example of "very experienced and highly qualified" consultants work. My girlfriend had a very rare condition caused by a crush injury at work and it took a number of consultants to reach not one, but several diagnosis ranging from vascular to cancer, and none were accurate. As a consequence, she had to take a number of painkillers which you only see in palliative care. It took her 10 years to finally pinpoint what it was and the tests were done at UCL London by a number of researchers and Professors.
Another cod example is the obesity epidemic and how medical physicians diagnose people with obesity simply by measuring the BMI (note I don't use the word "doctor" since doctor in latin means "docere" or "to teach"). If you think weight is an indicator to obesity, you are wrong and new research now points that sugar (namely Fructose) is the culprit for a number of reasons. Google search Robert Lustig Fat Chance 2.0 for UCLA lectures.
Just to clarify, my research is not what Doug does which is Chemistry, but one of my interests is what Katia Vega from MIT does in using nail technology with computer science and how can we interact with devices in the future by using everyday cosmetics.
The point I'm trying to make is that if you go with what your Consultant says and take it holy, by all means go for it. But also take it into consideration that in 10 years time, he MIGHT be wrong.