So am not a Garmin user (Apple) but for years now I will regularly wash my band with soap and water and regularly wipe the back of the face (the sensor part that comes in contact with your skin) with a cloth soaked lightly in alcohol.

If I am doing some outdoor work or a lot of exercise then I will always do this as well afterwards. My wife ran into some issues with her wrists after getting hers where she developed a rash and found that regularly cleaning of the watch - both band and the sensor area stopped this from happening.

I clean my Samsung watch with a wet wipe (the kind you use on human skin - like a baby wipe or "flushable" wipe -- which isn't, never flush those things), and dry the face/underside with a smooth microfiber cloth. The band I have is some form of leather, so yrmv.

My skin can't stand silicone bands so I stick to metal or leather.

I just let my dog lick mine clean from time to time.

I think dish soap is a great start. It’s mild and doesn’t have abrasives or harsh chemicals that may stain the watch. I have a Mk2i and that’s how I’ve cleaned mine when it needed it.

You may also have developed a mild allergy to whatever the back of your watch is made of, in which case cleaning won’t help.

Skin irritation is a pretty good sign that it’s about time to clean it.

If the wristband is made of silicon, you can just clean it with soap and water.

I think I’ve read somewhere that the watch itself should be washed with normal water instead. I guess there are some gaps and holes where soap isn’t welcome.

If you have a fancy metal wristband, soap will do an acceptable job, but an ultrasound bath would be better.

Garmin Forerunner user here.

I just wash mine with hand soap and water after each run or if I’ve been working in the garden - typically gets washed every other day.

Three years on, no problems here.

I get skin irritations regardless of how clean my smart watch is after my wrist gets wet. Not entirely sure why, but something to consider if cleaning doesn't help.

Check the manual to see if there are specific cleaning instructions. You don't want to accidentally damage any rubber seals with soap that's too aggressive or scrub off a protective coating somewhere.

My watch came with instructions to wipe it down with clean water, then some standard disinfectant alcohol. If that doesn't work, soap-free detergent is recommended (I didn't know that existed in any mild form?), so I'm guessing my watch really doesn't like soap.

I wouldn't mess with stuff like alcohol on rubber/silicone bands without checking if it doesn't melt the material. Accidentally making napalm by combining plastics and solvents is way too easy!

I rinse mine in iso, scrub with an old toothbrush and rinse.