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In summary: Redheads do appear to be less responsive to general anaesthetics, as far as if reported. However, either an increase and/or decrease to different types of painful stimuli is shown. Also, the mechanism for these results is still unknown, but is very probably related to the mutation in the MC1R which gives redheads their red hair in the first place.

In summary: Redheads do appear to be less responsive to general anaesthetics, as far as reported. However, either an increase and/or decrease to different types of painful stimuli is shown. Also, the mechanism for these results is still unknown, but is very probably related to the mutation in the MC1R which gives redheads their red hair in the first place.

However, this report adds that redheads were more sensitive to thermal pain, while less responsive to the common aesthetic lidocaine.

In summary: Redheads do appear to be less responsive to general anaesthetics, as far as if reported. However, either an increase or decrease to different types of painful stimuli is shown. Also, the mechanism for these results is still unknown, but is most probably related to the mutation in the MC1R, which is what gives redheads their red hair in the first place.

However, this report adds that redheads were more sensitive to thermal pain, while less responsive to the common anaesthetic lidocaine.

In summary: Redheads do appear to be less responsive to general anaesthetics, as far as if reported. However, either an increase and/or decrease to different types of painful stimuli is shown. Also, the mechanism for these results is still unknown, but is very probably related to the mutation in the MC1R which gives redheads their red hair in the first place.

This scientific article does in fact state that a mutation in the MC1R (which is what causes red hair) can also cause some sort of pain reduction.

Note: Emphasis added is my own.

This Wikipedia article which states a similar conjecture also adds:

In summary: Redheads do seem to feel pain at a reduced level in comparison to other humans, due to the mutation in their MC1R gene (which causes the red pigmentation in their hair in the first place). However, the mechanism behind this phenomenon isn't currently known.

• Mogil, J, J Ritchie, S Smith, K Strasburg, L Kaplan, M Wallace, R Romberg, et al. “Melanocortin-1 Receptor Gene Variants Affect Pain and Μ-opioid Analgesia in Mice and Humans.” Journal of Medical Genetics 42, no. 7 (July 2005): 583–587.

This scientific article states that a mutation in the MC1R (which is what causes red hair) can also cause some sort of pain reduction, as well as a lesser sensitivity to anaesthetics.

However, this report adds that redheads were more sensitive to thermal pain, while less responsive to the common aesthetic lidocaine.

Results: Current perception, pain perception, and pain tolerance thresholds were similar in the red-haired and dark-haired women at 2000, 250, and 5 Hz. In contrast, redheads were more sensitive to cold pain perception (22.6°C [15.1, 26.1] vs. 12.6°C [0, 20], P=0.004), cold pain tolerance (6.0°C [0, 9.7] vs. 0.0°C [0.0, 2.0], P=0.001), and heat pain (46.3°C [45.7, 47.5] vs. 47.7°C [46.6, 48.7], P=0.009). Subcutaneous, lidocaine was significantly less effective in redheads, e.g., pain tolerance threshold at 2000 Hz stimulation in redheads was 11.0 mA [8.5, 16.5] vs. >20.0 mA [14.5, >20] in others, P=0.005)

Additionally, this article states that redheads are significantly less sensitive to the anaesthetic desflurane.

The desflurane requirement in redheads (6.2 volume-percent [95% CI, 5.9 - 6.5]) was significantly greater than in dark-haired women (5.2 volume-percent [4.9 – 5.5], P = 0.0004). Nine of 10 redheads were either homozygous or compound heterozygotes for mutations on the melanocortin-1 receptor gene.

Lastly, this Wikipedia article explains...

In summary: Redheads do appear to be less responsive to general anaesthetics, as far as if reported. However, either an increase or decrease to different types of painful stimuli is shown. Also, the mechanism for these results is still unknown, but is most probably related to the mutation in the MC1R, which is what gives redheads their red hair in the first place.

Note: All added emphasis is my own.

• Mogil, J, J Ritchie, S Smith, K Strasburg, L Kaplan, M Wallace, R Romberg, et al. “Melanocortin-1 Receptor Gene Variants Affect Pain and Μ-opioid Analgesia in Mice and Humans.” Journal of Medical Genetics 42, no. 7 (July 2005): 583–587.

• Liem, Edwin B., Teresa V. Joiner, Kentaro Tsueda, and Daniel I. Sessler. “Increased Sensitivity to Thermal Pain and Reduced Subcutaneous Lidocaine Efficacy in Redheads.” Anesthesiology 102, no. 3 (March 2005): 509–514.

• Liem, Edwin B., Chun–Ming Lin, Mohammad–Irfan Suleman, Anthony G. Doufas, Ronald G. Gregg, Jacqueline M. Veauthier, Gary Loyd, and Daniel I. Sessler. “Anesthetic Requirement Is Increased in Redheads.” Anesthesiology 101, no. 2 (August 2004): 279–283.