nfshirley wrote:
I have this exact same problem that has only just appeared. …recently I have started to experience these small marks on my wrist underneath where I wear the watch.
That's certainly not overtly presenting as a thermal or radiation burn. That looks more like dermatitis or another skin reaction, but I’m also not a medical provider. Causes of dermatitis and irritations can include a mild allergic reaction, or can involve moisture and any of various skin fauna, or skin irritation due to chafing, or a mixture of these or other causes.
Superficial or partial-thickness burns and particularly those due to contact usually look, well, different from that.
Best approach here is a discussion with a medical provider. They have far more experience and training, and have access to various treatments if and as needed.
If you prefer to not get a medical consult, other options can involve cleaning both the Watch back and the skin, and then drying both throughly, and quite probably removing the Watch until that issue or irritation heals, or switching the Watch to the other wrist while that wrist heals. Check the tension on the band, as well. Both too loose and too tight can be bad.
For what Apple suggests for reducing or avoiding skin irritations, and for cleaning Apple Watch:
How to clean your Apple Watch - Apple Support