Apple Watch SE Sensor Burn

Hi all,

I have had my Apple Watch for less than a year and it was perfectly fine for a few months until I started getting red flaky and itchy skin. I left my watch loose and changed the strap but every time I put the watch back on the same thing was occurring. I let my skin heal and I’ve noticed a black circular scar has formed where the sensor sits on my wrist. Have I been burnt or is this an allergic reaction?