It’s basically colored vegetable oil. Kinda thick, but wipes off with water. Leave a heck of a welt on you even thourgh clothes. We call it “pepperoni” because that’s what the welts look like. Pepperoni slices. Very rarely cuts the skin. Leaves a pretty good bruise. Won’t even break glass.
My sons and I used to play all the time. As for pain and injury, things happen. We would have western-style matches, and it was to the pain: start about 50 yards apart walking and firing until someone cried uncle.
During one such battle, my son’s regulator glitched and he hit my thigh so hard that I had a black bruise that lasted for months. (I cried uncle and a few more unwholesome words.) I’m just glad the gun held together because they aren’t made for those pressures. Good times!