@ OP,
Just my bit to add, while it is also NOT to be considered as "MEDICAL ADVICE", however, from what you wrote, I understand it is nothing severe or at least it currently seems to rather be a minor discomforting issue. Obviously, everyone has to decide by themselves how long to wait or why and when it's time to seek professional medial care and treatment!
In my younger days I'd usually hesitate much longer and the threshold of severeness before to decide it's time to see the Doc was much higher than perhaps nowadays, or at least, let's say if it's my daughter who's suffering, I'd see the doctor rather sooner than later!
BUT again, in case of a "milder" sort of rash or localized skin irritation (like slight blistering on forearms), I'd firstly assume that the reason is highly likely due to excessive exposure like to strong sun or from contact with some sort of substance, it could be from accumulated dust and air pollution particles, which easily attach to sweaty skin, considering that both hands and forearms tend to be most exposed, compared to the rest of the body, except maybe the face.
But that would only be my first - but definitely not he final conclusion!
Anyway, I have found "J&J baby powder" to be something you can always try without taking any risks. Another universal SKIN CARE is fresh Aloe Vera, which you can find on every corner and is just as simply to apply without the possibility of doing anything wrong!
HOWEVER, if whatever it is you have, doesn't seem to quickly improve and no change to the better can be noticed soon, or if in fact it's getting even worse, I strongly urge to see a doctor AQAP!
The last thing you want is to go from a slightly itching rash, starting with a few seemingly harmless, tiny-little blisters, which through constant rubbing and scratching, can quickly develop into lacerations and just increase the risk of further infection, especially with all the germs that are omni present in tropical third world places like here in VN!
