Odd reaction...?

I was just pumping before going to bed, and some milk dripped on my arm, I wiped it off and continued pumping then I noticed where the milk dripped on my arm I now had and odd rash looking spot.. (Picture below) should I be worried about my son drinking my milk? Or could I somehow be reacting to my own milk..? I feel extremely stupid asking that..but I'm totally confused on why I got a weird reaction...