The same kind of effects, were noticed by me with use of a then-new
iBook G4 12-inch 1.33GHz (mid-2005) last model PPC, in the day.
My current early model MacBook1.1 has a similar trackpad, yet I
do not use it; instead use wired mouse & keyboard at a desktop.
As a result of this odd sensation that reminded me of some kind of
electro-static effect that caused nerve and joints to ache, I figured
early on it was not something to continue; since then I often use a
wired keyboard and mouse, with powered USB hub, with portable
Macs and that is much better on my hands.
The issue does not seem to be an allergic reaction as much as it
may be a form of sensitivity to the electro-static processes that
make the touch pad, trackpad, and maybe some touch iDevices
annoy a segment of the product user population. Sort of like a
few dozen per thousand who can't use a new PC or Mac, and
have to let them run-in a few dozen hours (unattended or in a
well-ventilated room) before they can stay in close quarters with
one. Not a form of insanity, just a specific sensitivity; instead of
dealing with electro-static or electro-conductivity, they get a form
of toxic exposure from chemicals. Older logic boards used to gas
off their residual chemicals after a time, as I recall some product
models, back in the day. Some said the effect was worse after we
started getting early products whose board were made in China
or Malaysia; the older Ireland-made Macs didn't do it, nor USA.
Back to the touch pad or trackpad. One could try to use quality
surface cleaner and then apply a protective film such as one
offered by this example; made for a variety of products, with
different surface effects. Could be one of these products can
be helpful to layer over original touch/screen surface(s) as a test.
http://www.photodon.com/c/LCD-Protective-Films.html
Though I've never tried this brand products, years ago considered
LCD screen protectors from them, due to the soft layering of early
LCD iMac G4 and iBook G3/G4s to protect them. However this
may be a useful idea at least for some percentage of users whose
issues could be resolved by such an item that clings on the surface.
Good luck & happy computing! 🙂