Once upon a time, Kingwood was used to manufacture extremely high end furniture. In fact it is believed that the common name of Kingwood is a reference to the fondness for the wood expressed by the French Kings Louis XIV and Louis XV.
Sustainability
Kingwood is not listed as being in any way threatened or endangered by the Convention in International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendices nor does it appear on the International Union for Conservation of Nature (IUCN) Red List. However, I would not be at all surprised if this were to change in the near future as Brazil moves more and more to protect its natural species which have been heavily exploited for centuries.
To the best of my knowledge, Kingwood is not subject to any special restrictions by any United States government agency.
I realize that inherent in working with wood is the killing of a part of the natural world that may be slow to return and if I become deeply concerned about this fact, I will have to find a new hobby. I hope that such a time does not come to pass or at least not any time soon. In part because I am concerned about legally and responsibly obtained wood, I am reluctant to buy from sellers outside of well-established and known vendors. I am highly unlikely, for example, to purchase any wood from auction sites, such as Ebay, because of uncertain sourcing and documentation, as well as the potential, even likelihood, of material being misidentified in order to achieve a higher selling price.
However, due to the commercial scarcity of some domestic woods, resorting to auction sites such as Ebay or Etsy may be the only way to obtain some desirable domestic, or in some cases exotic imported, species that are not routinely commercially harvested. The potential risks of buying in these marketplaces have to be balanced against the desire to work with a specific species of wood. That is inherently an individual decision.
I also realize that many, if not most, wood workers do not have endangered species lists memorized, therefore I think it worthwhile and important to do even a small amount of research before purchasing any lumber, domestic as well as imported, to be certain of the potential impact you are having, even in a small way, on threatened or endangered populations. This information is easy to come by and takes only minutes to locate through any Internet search engine, including those you can access on your phone as you are standing in the lumber yard or store. Unfortunately, you simply cannot count on a vendor to tell you a product they are selling is endangered.
Health Hazards
Kingwood is not known to commonly cause any severe allergic or other adverse health reactions, but it can act as a sensitizer, such that the more one works with Kingwood the more sensitive to the wood one becomes. That said, the most common sensitivity reactions are relatively mild and consist of simple eye and skin irritation as well as the occasional case of pink-eye.
In addition, the long-term negative effects of exposure to sawdust of any species are well documented.
It is important to remember that although many people may, or may not, be sensitive to any given wood the only experience that truly counts is your own, so use reported side effects as guidance but not as a substitute for cautious and safe practices.
Appropriate protective equipment is therefore always recommended when working with this, or any other, wood, exotic or domestic, unless you have worked with the species before and are certain you are not sensitive to it.