Ok guys I'm sick of dealing with this so I'm coming here for help. I've been riding my 5 year old in a few different bits and every one of them cuts/rubs the sides of her mouth. I have gone through an O-ring, D-ring, loomis gag, tender touch, and a junior cow horse. I dont claim to be the lightest handed person but I am not heavy. My other horses have never had sores on their mouths. For the last 3-4 months I have been lathering up the corners with vaseline which helps a tiny bit but they are still pink after I ride her. I ride with bit guards...doesnt seem to matter. Has anyone experienced this before? This horse is overly sensitive about everything so this just gets added to the list. Honestly, at this point I feel like I'm going to have to move her to a hackamore so she doesnt start hating her job. Any ideas??

Your bit might not be wide enough for that horse.’

you can try wrapping the the outer edge of the mouth piece with Sealtex. ( buy it at Bug Dees).

I would put her in a bosal or a hack untill those raw places heal up completely and then some and then try with the widest bit you have and see how it gos from there, sometimes bit guards can make your bit tighter, so I would look at the guards and see what the bit looks like with and without the guards.

Edit to add, maybe even go with a sidepull untill her mouth heals..

This has also crossed my mind but the interesting thing is that this horse is tiny. She is 14.1...on a good day. Plus I feel like the bits fit in her mouth good. Not too wide either.

I gave her three months off over the holidays because I thought the same thing..maybe they just hadnt had enough time to heal all the way and were just reopening. First ride back, corners were pink again. I will take a look at the bit fit for sure. But I think you may be right right that maybe its just time for a change of headgear and go from there. I dont have a side-pull on hand but I probably need to invest in one.

maybe loosen her headstall a notch? 

I had a mare that was this way with every cinch I used on her I tryed so many different ones and they all rubed her raw behind her elbows, she was just so darn sensitive, so maybe this is your horse too just super sensitive skin around her mouth.. I had to watch some bit guards that I use as they would make my bits tight and would rub..

Maybe the bit is too wide so, like in the case of a one piece broken bit (snaffle) the sides are coming up too far.  Especially if you have enough room for bit guards as well and it's still happening. 

Do you have any pics with the bit in her mouth? 

You can find info and instructions on line to measure your horse's mouth... i have a couple of horse's that cannot wear your standard 5" mouthpiece because it isn't wide enough for them.

I would just wrap the outside part of the mouthpiece (that’s in the corner of her mouth) with Sealtex. That should take care of it.

It’s $6 for a roll that will do several bits 

https://www.bigdweb.com/product/sealtex+bandage+%28bit+tape%29.do?sortby=bestSellers&refType=&from=Search&ecList=6&ecCategory=

Is she a stiff horse? Does she pull on you at all? 

My 5 year old is the same! Her bits fit, and all have bit guards. I’ve been watching my past runs and if I slightly make contact with her mouth at the back of a turn, she throws her head up. I’m almost convinced she’s anticipating that. I have her teeth checked every 6 months. 

I think I’m going to try her in a hackamore.