kay wrote:
Hydrogen peroxide might be of use - it will fizz up and the thorn will
possibly pop out.

Bread poultice is good for that. But I think the OP had already got the
thorn out - his problem is whatever muck the thorn carried in with it.

Yup. Eventually went kind of Janet's way - had a hot bath and then dug the
whole surrounding area out with my nails whilst it was all still soft and
pliable. Not the most sensible idea, but it was getting annoying, and it
seems to have worked. I now have a very small scabbed over bit and no
inflamation. Yay.