Q. What's in a skunk's juice that makes it smell so bad?

M.L.

Peabody

A. William Wood, a chemical ecologist at Humboldt State University in California, risked his nose and the possibility he'd never be invited to another party in order to come up with the chemical formula of skunk spray.

In a word, he says, the answer is thiols.

Wood says the major components of the two or three grams of spray in a skunk's sac are 2-butene-1-thiol and 3-methyl-1-butanethiol, which consist of sulfur, hydrogen, and carbon atoms. The sulfur and hydrogen atoms are bonded together. That explains why eau de skunk is so repugnant.

In our noses, they attach to the same smell receptors we use to detect a similar chemical, hydrogen sulfide gas - which we know as that "swamp gas" smell. Hydrogen sulfide is more toxic to mammals than cyanide, Wood says, so we evolved particularly sensitive receptors to let us know when it's around.

Skunks learned through evolution that the best defense is a very offensive offense. "The 'Go Away' message is very profound," Wood says. We can smell it at concentrations as low as 10 parts per billion.

In high concentrations it can bring on vomiting or even cause the victim to lose consciousness; sprayed in the eye, it's like tear gas.

Skunk spray has never been known to be fatal, though it can certainly kill your friends' desire to be anywhere near you.

Thiols are not volatile, which means they don't evaporate quickly. That's why the smell lasts so long. Secondary chemicals in the spray break down into thiols in the presence of water, so washing actually makes things worse.

If you're sprayed, the best way to get rid of the smell, Wood suggests, is to change the chemical composition of those stinky thiols with the following solutions:

For pets, mix a quart of 3-percent hydrogen peroxide (from the pharmacy), a quarter-cup cup of baking soda, and a teaspoon of liquid detergent. Your brown-haired beagle may turn into a bleached blond from the peroxide, but at least he won't smell.

For you: same formula. Same warning about bleaching your hair.

For clothes: one cup of bleach per gallon of wash water.

The folk remedy of tomato juice doesn't really remove the smell. It overpowers it after your smell receptors become overloaded with thiols, so you end up smelling the tomato juice. Eau de skunk is still there.

Your best bet is to avoid being sprayed in the first place. Stay at least 15 feet from any skunk you happen upon. That's safely out of their range.