It’s called contact dermatitis, I had this when I tried sleeping with my watch (basically wore it 23 hours a day). Once I returned to charging it overnight and cleaning the watch regularly - it went away.
Try loosening the watch strap & cleaning the watch + strap with isopropyl alcohol.
If it continues - consult a doctor, not strangers on the internet.
It’s called contact dermatitis, I had this when I tried sleeping with my watch (basically wore it 23 hours a day). Once I returned to charging it overnight and cleaning the watch regularly - it went away.
Try loosening the watch strap & cleaning the watch + strap with isopropyl alcohol.
If it continues - consult a doctor, not strangers on the internet.