Arms chaffing when running

[CarrotPuff]

My arms started to chafe just above the armpit (if you lift your arm up) when going for long runs. I feel like they are rubbing against the seam of the t-shirt?

Thing is, I've been running in the same bra and T-shirt for the last few months. And it's never caused an issue. I ran 12 miles a couple of weeks ago, and was absolutely fine. Done 14 last week, and that's when it started. But not in the last 2 miles, kind of a few miles in. Doesn't happen on shorter 5m runs.

What on earth could it be? I haven't put on or lost any significant amount of weight, my arms aren't more muscular either, so why the sudden change?

Has anyone had this happen to them? What can I do? Putting Vaseline before run didn't help, and I don't really want to run in T-shirt with sleeves...

I get this from time to time too - Body Glide does the job! I think all runners experience this, especially on longer runs.

Seams getting worn?

I had this. Have you shaved under arms before runs? Could be stubble rash? Mixed with sweat?

I get this but just on my right arm for some reason and only on longer runs. Body Glide stopped it immediately

I've had this on long runs a couple of times, but not others, no rhyme or reason to it either! Have you tried a vest rather than a T-shirt?

I occasionally get it on long runs/ HMs.

Have you had any lockdown weight change causing clothing to get more loose or snug?

Thanks everyone, I'll try body glide!

@ThickFast definitely not stubble, they were freshly shaved today!

@HowFastIsTooFast I'm not sure what you mean, it's a sports racer back vest, so no sleeves.

Change to a tight-fitted sleeved top, that'll prevent chafing.

Aah ok @carrotpuff, I have both racer back vests like that and proper t-shirts with short sleeves, most of my chafing has happened in the t-shirts but I've also had it once with a vest where the inside of my arm was rubbing the armhole seam of the vest. That was when it was raining heavily though, so the vest was stuck to me and seam probably protruding more than usual.

I get this when running in hot weather - I assume it's a mix of the arm pumping action and sweat, it only happens when I wear sleeveless t-shirts. A dab of vaseline sorts it out.