What causes red welt under armpit?
Thanks for the query.
It is looking like contact dermatitis.
If you see carefully both the welts are on apposing sides.
I treat such cases with a topical steroid cream like fluticasone and anti histamine tablet.
I have seen excellent response with these.
You can try these in consultation with your doctor.
Let me know if you have any other doubt.
As I mentioned it is an allergic condition.
A single cause cannot be determined.
You might be allergic to various things like dust, pollen, cloth etc.
There is nothing to worry.
It's a common thing.
Just apply a mild steroid and take an antihistamine tablet.
You will be relieved.