Question: how do you know if you're allergic to poison oak?
Answer: If you're allergic to poison oak, signs will begin to appear 1 to 6 days after exposure. Most of the time, you'll notice it within the first 24 to 48 hours. The most obvious evidence of an allergic reaction is skin rash, also called dermatitis. First, you may notice some stinging, itching, and minor skin irritation.