Conditioning challenges are interventions that sensitise the peripheral nociceptive system in such a way that the nociceptive system either responds more vigorously to noxious stimuli (hyperalgesia) or responds to non-noxious stimuli (allodynia). The manner in which that peripheral nociceptive system responds provides important information as to the physiological functioning of the peripheral nociceptor system. The investigators will apply established conditioning challenges to the subjects' skin. Topical application of capsaicin and mustard oil are all well validated, established and safe conditioning challenges that sensitise peripheral nociceptors. Prof. David Bennett's group has extensive experience in using both conditioning challenges. In the only study to date investigating alteration of peripheral fibres after a conditioning challenge in heritable pain syndromes, mustard oil caused an increased area of hyperalgesia in individuals with Familial Episodic Pain Syndrome as compared to unaffected individuals. Applying these stimuli could lead to minor skin irritation and that is they will not be used if there is a history of skin allergy/sensitivity. In practice having performed such tests hundreds of times this has not been a problem.