Anesthesiologists have long suspected that redheads require more anesthesia than other people. See more genetics images. Carsten Koall/ Getty Images

It's bad enough that redheads -- or gingers, as our British friends call them -- may one day be extinct. Now we find out that people with red hair need more anesthesia than other people, too. A 2002 study conducted by researchers at the University of Louisville in Kentucky, proved what anesthesiologists -- doctors who oversee the administration of anesthesia -- have believed for some time, that redheads are more difficult to knock out.

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Researchers at the University of Louisville chose 20 test subjects -- all women aged 19 to 40 -- 10 were redheads, the other 10 were brunettes. The dark-haired subjects were in the control group.

The researchers chose only women to cut out any possibility of gender playing a role in the study. They also chose women whose menstrual cycles were in sync, since increases in hormones can also play a role in susceptibility to anesthesia.

All 20 women were given desflurane, a common gas anesthesia. After the anesthesia took effect, the researchers gave each woman electric shocks, using a voltage which a conscious person would have found "intolerable" [source: Medscape]. If the subject could feel the pain, the researchers increased the dosage of desflurane and continued to administer shocks until they got no response to the shocks.

The researchers' findings showed that the old anesthesiologists' adage is true: Redheads do require more anesthesia. In fact, it took an average of 20 percent more.

Anesthesiologists have a dangerous job, and it takes a large degree of skill to properly put someone under. Too little anesthesia, and you have a patient who may wake up as a result of the pain from the surgery. Patients may also be able to recall the surgery when they awaken. Conversely, too much anesthesia and the patient may overdose, slipping into a coma, or even dying.

So while the experiment may sound cruel, it provided anesthesiologists with useful information to treat their redheaded patients. The pain endured by the redheads in the University of Louisville experiment may result in less pain for millions of other redheads who must undergo surgery. This characteristic isn't found only in redheaded women, however. A 2004 study showed that redheaded men and women alike require more anesthesia than their counterparts [source: Consumer Reports].

So now we know that redheads need more anesthesia. Read the next page to find out about the role genetics play in making redheads tough to knock out.