Jewelweed for Poison Oak?

I have read that Jewelweed helps in relieving poison oak rash when applied to skin. Can it be made into a tea and do it's work from within the body also?
Are there any Herbs that can be taken to build an immunity against this allergic reaction to Poison Oak?

The allergic reaction to poison ivy, poison oak and poison sumac is not well understood. Some people do not have allergic reactions. Once a person has had a reaction, they continue to react with future contact. I don't know of any safe methods of building the immune system to avoid future reactions. There have been recommendations to take a pinhead size piece of poison ivy internally to build immunity, but this can cause a systemic case of poison ivy, which can be fatal.
Jewelweed is usually used externally. There have been cases of allergic reactions to jewelweed when taken internally, so I do not recommend it.
Probably the safest method of dealing with poison ivy is to wash contaminated skin and clothing immediately in very hot, soapy water to get rid of the oils. Take care not to contaminate other clothing or other parts of the skin. Taking a shower will spread the poison oils to other parts of the skin. Treat any skin irritation immediately with fresh jewelweed or frozen jewelweed tea, or with a baking soda paste. The irritant in poison ivy, oak and sumac is urushiol, a phenol, which is neutralized by a base like baking soda.