Hi @lilyn You have my sincerest empathy for the itching you’re going through. I swear itching was worse than pain when I was dealing with it!
Unfortunately, itching can be a symptom of some forms of blood cancers or conditions. Especially PV where you have too many red blood cells. It may not necessarily be the HU. Though it’s suspicious that the itching increased with the dosage.

You’re not alone in this…misery loves company? Other members have written in and discussed the itching issue. Here is a link to the search for multiple conversations. https://connect.mayoclinic.org/search/

There is one personal note. Speaking with an allergist recently, we discussed this similar situation. He mentioned if there is a high level of eosinophils associated with the chronic itching sometimes taking an over the counter H2 medication (histamine blocker) such as Tagamet (cimetidine), Axid (nizatidine) or Pepcid (famotidine along with an antihistamine can be helpful. Something to talk about with your hematologist. Do you recall if your eosinophil level was elevated?
What was the reason your doctor increased the HU?