If you experience irritation or discomfort on your skin around or beneath your watch and/or band, Apple recommends that you remove your watch and consult a doctor/physician before wearing it again.
Discomfort or skin reactions can be a result of various causes, including:
Allergies (e.g., to nickel).
Extended exposure to irritants (e.g., soap or sweat).
Wearing the band too tightly or too loosely.
A small number of people will experience reactions to certain materials. This can be due to allergies, environmental factors, extended exposure to irritants like soap or sweat, and other causes. If you know you have allergies or other sensitivities, be aware that the Apple Watch and some of its bands contain the following materials: Nickel and Acrylates