I replanted several this weekend. Wearing leather gloves. Leather gloves are like butter to those needles.
Every once in a while you'd see a cowboy fall off his horse into a mess o' cactii in the old Westerns. I got to tell ya, that dude was in hell for a LONG time. Unless he happened to travel with tweezers and maybe a magnifying glass.
I had unimaginably tiny spines in me. You could only see them in profile. Anything that thin should break, but apparently skin is more porous than we think. Best advice: leave cactii alone.