Fig. 2. Graded responses to a range of von Frey hairs, shown as mean ± SD. ( A ) Applied to intact, uninjected skin with the same pattern and frequency as used to test for postincisional pain (n = 6). A significant stimulus-dependent hypoalgesia occurs during frequent testing by intermediate-sized von Frey hairs. ( B ) Applied to skin after injection of vehicle (n = 7). # P < 0.05 versus baseline of responses that were tested daily on the preceding 3 days, indicated by the points graphed in negative time. Responses were significantly greater than baseline values only during the period of frequent testing (0–5 h) and had returned to baseline by 24 h. von Frey hair forces were 18 (▪), 36 (○), 90 (▴), 143 (▿), and 520 mN (♦).