There are several studies that suggest that cannabis is may be an effective treatment for several dermatologic conditions, including prurits (itch).
In a 2003 clinical study, researchers concluded that in peripheral administration of a cannabinoid receptor agonist attenuates histamine-induced itch." Researchers used the synthetic CB1 (cannabinoid receptor 1) agonist HU21 — THC is a plant-derived CB1 agonist. Interestingly, HU210 did not reduce histamine levels. Rather, when the CB1 receptor was activated, it prevented the signaling of the nerve itself after histamine had already bound its receptor.
In a 2002 clinical study, researchers found that three weeks of topical application of a cream containing our own cannabinoids (endocannabinoids) dramatically reduced itch from uremic pruritis (caused by kidney failure).
In a 2002 clinical study evaluating the efficacy of THC in treating patients with severe itch caused by cholestatic liver disease, researchers found that nightly administration of 5mg of THC resulted in reduced itch and better sleep.
I generally recommend topical creams containing both THC and CBD, such as
If the itch were generalized or covering large areas, I generally would recommend a tincture, oil or edible with a moderate concentration of THC — ratio between 3:1 and 8:1, such as
I hope this helps!