--natural consequence of doing just too many drugs. Chemical burn gives you a metallic, grainy feeling in your brain, it is sometimes accompanied by a headache and light sensitivity.

You may also feel like your brain is short circuiting when it tries to do routine things, like take a shower (ummm...soap? Why is the soap in my hand?).

After a round of whatever your vice is, chemical burn sets in and you not only wonder why you consumed said vice, you start to convince yourself to not do it again.

Chemical burn usually lasts until you have had at least two good sleep sessions.

In a more physical sense, when one spills a corrosive substance onto one's skin, causing pain and usually a nasty scar. Some things that will burn you chemically: various acids, chlorine should probably do some damage and lye has recently been popularized by Fight Club. Basically anything on the extremes of the pH scale.

I recently experienced a mild burn on the tips of my fingers from Hydrochloric Acid and it was nothing to screw with, even on a small scale.