Antipruritic effects of Botox on histamine prick test and itch will also be assessed in parallel with the experiment 2. In this sub-experiment, 5 Units of Botox will be injected intradermally in the middle of volar forearm. The same volume of placebo will be injected into the other side. Histamine prick test will induce itch and the effect of intradermal Botox will be assessed compared to the baseline. Flare area and visual analogue scale (VAS) ratings will be measured.