From the same authors who brought you the New Sexual Femunculus:
Whipple B, Martinez-Gomez M, Oliva-Zarate L, Pacheco P, Komisaruk BR. Inverse relationship between intensity of vaginal self-stimulation-produced analgesia and level of chronic intake of a dietary source of capsaicin. Physiol Behav. 1989 Aug;46(2):247-52.
Women who chronically ingest a diet rich in capsaicin, the pungent ingredient in hot chili peppers, showed a significantly lower magnitude of analgesia in response to vaginal self-stimulation than women with relatively low or medium levels of ingestion. Vaginal self-stimulation-produced analgesia was quantified by measuring (on the hand) pain detection thresholds, pain tolerance thresholds and tactile thresholds. Whereas vaginal self-stimulation produced a 32.6-43.8% increase in pain detection and pain tolerance thresholds in the low chili diet group, it produced only a 2.3-7.3% increase in these measures in the high chili diet group. The medium chili diet group showed an intermediate effect on the pain thresholds. Tactile thresholds were not increased by the vaginal self-stimulation. Baseline (no stimulation) pain thresholds did not differ significantly among the three groups. These findings are consistent with earlier studies in laboratory rats, in which capsaicin administered neonatally abolished vaginal stimulation-produced analgesia, but did not affect baseline pain thresholds to mechanostimulation.