Jonathan; the information was quoted from the cited link; my brain does not retain that type of information; and no, I can not even name the trees that surround my house .
Ellery; when doing my search, I found reference to the allergic reactions in a couple of places. In one such reference the context was in working with the wood, i.e. sawing, sanding, etc. Thus my initial thought was that a finished surface might not be a problem. However, after reading your report, I don't know. It will be interesting to see what Jonathan is able to find out. It just seems to me that if fretboards could cause such a problem, we would have heard about it from 15% of Excel owners.