An update on my last post - beware the manicure. I did get cellulitis after a manicure - probably not even the salon's fault - pushing down cuticles even with clean implements may be enough to let the sort of germ that would not normally cause any issue at all into the body and the arm is simply not well enough defended. Once I twigged what it was (bit slow there!) it was easily fixed by antibiotics and I was actually quite pleased that it had started to resolve without treatment - something's still working! Been fine since, but don't want to do that again.