Peanut allergy? 2 hours later?

Tried a little peanut butter in formula today...probably 1/2 teaspoon mixed into 1/2 oz of formula. He was fine at first and loved it but just noticed this rash.

LO has sensitive skin but doesn’t usually have multiple spots like this at once and that appear quite so red and raised.

Dr said 1/2 teaspoon of Benadryl if the rash spreads and ER of signs if breathing issues. His thoughts tho we’re that 2 hours is late for a peanut reaction. Said to try again in a few weeks and if it happens again wait til 1 year.

We noticed it right as we were starting to give some banana which he’s had before. Wondering if maybe the banana made it worse? How are y’all doing with food allergens?