Garmin 945 skin rash/burn

very strange!  I would think it is an allergic reaction or some sort of heat/infection type irritation...  would think hydrocortisone lotion would be the way to go and maybe calamine would help .  Aloe possibly as well.  

when I had skin allergy issue from detergent mainly in the shorts area, by the time i figured it out it took many weeks to heal.  they gave me a higher strength cortisone type gel at doctor.   still took at least 5-7wks to clearup mostly... like 2mo until clear

See a dermatologist, he can advise and provide a prescription for the required lotion, certainly cortisone of some kind (free stuff won't help in this case). I've also been allergic to the standard 945 strap (blue) but in your case, this doesn't look like the strap as it's basically the watch area. Maybe there was some dirt or something between the watch and your skin and some kind of infection started. Clearly a medical issue though and not something for a technical forum.

Hello. Same thing happend to me! A week or so it started to itch as *** and the skin quickly got very red and dry. I don't know for sure but I suspect that it may be nickel present in the pins? It's known for its sensitising properties and it isn't allowed to be present in wearables having direct and prolonged contact with skin, at least not in EU, if the degree of nickel release from parts of these products that are in direct and prolonged contact with the skin is higher than 0.5 μg/cm2 per week.

I had the same issue. After stopping wearing it in the shower and giving it a weekly clean with anti bacteria hand soap the issue has gone away

I've had the same problem a few times, even though I regularly clean the watch with dish soap or isopropyl alcohol. I don't have any known allergies.

When it happens, I take the watch off as much as possible or wear it on the other wrist.

There are some little "silicone anti dust caps" you can try. They cover the connector at the back. I think you have an allergic reaction to the connector (metal parts) and with this you could avoid this. I also have this covers and they work well and the connector is also protected from dust and sweat. Hope this helps. If it is allowed, I could also post a link from ebay germany but I think you could find them anywhere.

Wash your watch in soapy water whenever you shower. I do mine after every training sessions. Takes seconds. Don’t put it back on until both it and your skin is dry. 
Once a week is not enough. 

I don't think he needs further advice here after over three months...this topic should be closed.