Figure 1.

Intradermal injection of β-alanine evokes itch in humans. A, Time course of the mean perceived intensity of itch and nociceptive sensations evoked by intradermal injection of 90 μg (100 mm) of β-alanine or l-alanine. The mean ratings of itch, pricking/stinging, and burning obtained from 11 subjects are plotted for successive intervals of 30 s after injection. Beginning with the peak rating of each sensory quality, the SEM is plotted every 5 min (error bars). The positions of three verbal descriptors (vertical scale on the right) are shown in correspondence with the ratings of mean perceived intensity (y-axes). B, Time course of the mean perceived intensity of itch and nociceptive sensations evoked by different doses of β-alanine and l-alanine in the same subjects.