Skin irritation vivosmart4

It's possible that you're allergic to the band material - some silicones might be irritants to some people even if they're generally considered non-allergenic. It's also possible that you're exposing your band to an uncommon environment that's causing it to degrade unexpectedly (or that quality control isn't 100%, and some percentage of bands tend to degrade more rapidly on their own), which can result in potentially irritating compounds forming, though this isn't usually a concern under normal conditions (I'm not sure what all catalyzes silicone degradation, but acidic or alkaline environments are common catalyzing environments, as acids and bases are oxidizing and reducing agents, respectively).

The smell indicates a buildup of something. Unless you've had a recent change in diet or environmental exposure to some chemical to which you react badly (new municipal water supply, recently started smoking or drinking alcohol - or doing so a lot more, recently starting drinking a bunch of energy drinks, etc.), it's seems unlikely that the problem is buildup of something that's excreted in your own sweat or sebum, else you would have seen similar issues with other bands. Still, it's possible that the other bands didn't trap sweat/sebum in the same manner. If you've recently changed soaps or skin lotion, it's possible that one of those is the irritant, but only when it's trapped in sufficient concentration for a sufficient duration thanks to the watch band, so the irritation is only occurring there. If it's a sort of rubbery/chemically smell that persists even when you haven't been wearing the watch, that sounds very much like the band material degrading.

If it doesn't smell when you haven't been wearing it for a couple of days, then the buildup has something to do with contact with your skin. It's most likely that the (moist, anaerobic) area under the watch band or the irritation that's it's causing is making your wrist a nice home for some smelly bacteria, and irritation could result from their activity in addition to physical irritation/chafing. If the smell is a rotting, fishy, musky, or sour earthy smell, then it's very likely bacterial. If you're washing the band daily and keeping it and your wrist dry when you're not exercising (obviously can't do so while sweating heavily), try cleaning it with isopropyl alcohol (I recommend using a cotton swab so you can really work the alcohol into the seams and impressions on the bottom of the watch to thoroughly clean it) and then letting it sit in direct sunlight with the inner surface of the band completely exposed for half an hour to an hour; this should help sterilize the band and kill off any bacterial colony that managed to get lodged securely in an indentation where it's not being removed or killed by regular washing with soap and water.

Just to make sure, when you say you've tried wearing it loose, how loose? I ask because I wear my watch 24/7 except to charge it every few days, and I had irritation issues when I was wearing it exercise-snug all the time; now I tighten the band one or two notches for exercise (depending on what exercise I'm doing - if I'm biking I only tighten it one notch, because my arms don't move much, but if I'm doing something where I'm moving my hand/arm around a lot, then I tighten it two notches or it won't consistently get a good reading) and wear it looser the rest of the day, usually sliding it a bit farther up my wrist so it's still snug enough for a reading during low-impact activity all day. In my all-day wearing, it's loose enough that I can slide my index finger between the band and my wrist if it's at the thinnest point of my wrist.

Conversely, if it's TOO loose, it may be sliding around and chafing more than it would if it were slightly tighter and staying in place better; I learned the trick of sliding the band a bit up my wrist so it won't move during low-impact activity, while still being looser than needed for high-impact activity, because I was running into some irritation with it sliding around when too loose after compensating for it being too tight before. A number of other posts I've seen about irritation look a lot more like physical irritation from rubbing than any sort of chemical irritation, and that can be an issue with band fit in either direction. Again, I assume you've checked all of this, but because "loose" and "tight" are relative terms, I wanted to double-check with the specifics of what worked for me.

Final thing to check is make sure you're drinking enough water. Dehydration results in skin being more susceptible to damage, and it can thus contribute to the irritation in a number of ways, whatever the root cause is.

I started wearing mine 24/7 in February 2019 and after about 6 months I started getting a rash and reactions.  It would come back just hours after putting the strap back on. I took a 6 month break and now I've been wearing it again for 3 weeks with no issues.  I do wear it kind of lose and really watch when I wash my hands to not get water on or under the band. 

Hi, I apologize you have experienced this issue. Can you please reach out to us directly at support.garmin.com for assistance. We would like to get this resolved for you.

I just found this thread but wanted to say I have the EXACT SAME PROBLEM. I even stopped wearing mine for a year or more and STILL HAVE THE PROBLEM after wearing about 48 hours. Did you ever find a solution? 

Gave one as a gift to my wife but she had irritation from wearing it and refuses to use it any longer. I was looking to see if there was any aftermarket solutions to the Garmin runner bands, but the design makes it impossible to make any alternative bands like metal bracelets which I've gotten for my Fitbit.  The clasp for the rubber band protrudes quite a bit so it digs into the wrist if it's not left really loose, so it's not very forgiving as to how tight it can be for better measurements vs loose so it doesn't cause an imprint in the wrist.

I wonder if there was any reason for the design that makes it a throwaway product if the rubber band breaks or is otherwise unsuitable for the user.  I'll have to see if this needs to be returned.