When I was young, I had a terrible time with poison oak reactions. If they burned it in the town I lived in, I would get it just from the oils floating in the air. I would get blisters all over my body, as well as down my throat and up my nasal passage.
We had two goats at the time that we used for milk. They would roam around the woods and eat shrubbery, (and poison oak!), and over time I built an immunity to poison oak from drinking their milk. I can wade chest high in the stuff with no reaction now, and it’s been 30 years since I developed the immunity. I would say the best way to desensitize yourself is to drink the milk of goats that have been eating something.