No. They do not have the toxins in their skin but some have in their eyes an other parts of their body.
A very small amount - yes.
if you are referring to spider man toxin is a spawn of carnage witch is a spawn of venom. but a real one is a poison that is fatal
Toxins are poisons. They may be natural or manmade.
Yes. Skin is the largest organ in the body and excretes toxins via sweat.