Horse sore “arm” pits

[ahlam1399]

So horse decides to throw something else at me that I?ve never seen before. Appears quite sore in the ?armpit? area, underneath his chest/behind legs. Doesn?t appear red or inflamed, but there isn?t much hair in there. On both sides. Got rather grouchy when I had a better look/feel at it, so presume it?s a bit sore.I?ve put some Vaseline wondergel type stiff on it, as it was all I had to hand at the time. He is out 24/7, no mud in there, and not sweating. Any thoughts?

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