Hi
If you experience redness, swelling, itchiness or any other irritation or discomfort on your skin around or beneath your watch or band, then Apple recommends that you remove your Apple Watch and consult a doctor / physician before wearing it again.
Some people, for example, can experience reactions to certain materials - such as nickel - that are in prolonged contact with their skin.
Skin reactions can be a result of various causes including:
- Allergies (eg to nickel).
- Extended exposure to irritants (eg soap or sweat).
- Environmental factors.
- Wearing the band too tightly or too loosely.
More information, including tips from Apple:
Also be sure to follow Apple's handing instructions in respect of operating temperatures:
Keep Apple Watch within acceptable operating temperatures - Apple Support
If you are concerned about a potential hardware defect, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance:
Source: Issues with Apple Watch burning wrist. - Apple Community