The heat/capsaicin sensitization model: a methodologic study

The heat/capsaicin sensitization model induces cutaneous sensitization by using a combination of heat and topical capsaicin. It has been suggested that the stability and duration of the cutaneous sensitization are due to a synergistic effect between heat and capsaicin. The aim of this study was to evaluate a possible synergistic effect between heat and capsaicin in inducing cutaneous sensitization. Twenty healthy male volunteers completed this random order, 4-session study. Three different stimulation combinations were used to induce cutaneous sensitization: day A, heat and capsaicin; day B, heat alone; day C, capsaicin alone. Combination A was repeated on day D to determine between day reproducibility. Rekindling was performed 3 times at 40-minute intervals to maintain stable areas of secondary hyperalgesia. Brief thermal sensitization (45 degrees C for 3 minutes) was induced at each session. Within and between day reproducibility was calculated. There was no difference between the size of areas of secondary hyperalgesia after stimulation with heat/capsaicin compared to heat and capsaicin stimulation alone. The within day reproducibility was better with heat/capsaicin than with either stimulation alone. There was no synergistic or additive effect between heat and capsaicin in inducing cutaneous sensitization. Rekindling seems to be the important factor in maintaining stable and long-lasting cutaneous sensitization.