Rash under watch sensor section

I have been wearing a 38 mm face aluminum case series 2 watch since July 2017. I wear it on the underside of my left wrist to prevent hitting the face on walls. I wear it most the time except when showering, including at night. I have had any skin reactions until yesterday. This page won’t let me post the image but it is similar to the size of the sensor face of the watch. I wiped down the watch and band with isopropyl in case it was poisen ivy and I’m wesring on my right wrist for 24 hrs without a reaction. I don’t know of any metal allergies. I wear a Milanese band with the tension enough to keep it still with a slight pressure mark left when removed.