Welcome back @esperanzam. You'll notice that I moved your message to this existing discussion about Essential Thrombocythemia and the side effects of hydroxyurea. I did this to reconnect you with fellow members like @huronshores @mjpm2406 @lefsequeen @tresman10 @cblowers1 @claire39 and @shenriq. Perhaps others have had experience with blistering skin on the feet. According to to this article by Mayo Clinic blisters on skin is listed as "incidence unknown" meaning it is quite rare.
– Hydroxyurea (Oral Route) https://www.mayoclinic.org/drugs-supplements/hydroxyurea-oral-route/side-effects/drg-20068109

How are they suggesting to treat your foot?