help, sore on mouth !

I noticed today that gypsy has a sore on her mouth. Its on the corner of her lips, right where the bit goes on the left side of her mouth, but not on the right. I feel HORRIBLE.

She wears a happy mouth bit and I have heard that rubber bits can cause sores if your horse has a dry mouth. Gypsy always foams/salivates a lot when I ride so im not convinced that is why, but it still could be because its rubber I suppose. The bit itself is in good shape but there is a bite on it from when I was using it on my other horse.

Any advice ? I was thinking of putting vaseline on her mouth and maybe trying to find her bit in metal.

Vaseline is a quick "help" but not a cure. There are a few reasons why a sore could be developing:

1. Bit is not long enough for horses mouth. Should have about 1/4 inch on BOTH sides of the mouth between the end of the bit and the horses lips.
2. Depending on bit type (like loose ring snaffle) the corner of the lips could be getting pinched by the bit. In a loose ring there is a hole in the bit end where the ring goes through. Sometimes part of the lips ca also get caught therte. A "D" ring or egg butt snaffle don't have an area where the klip skin can get pinched - so are a good alternative.
3. Horse could be allergic to that type of metal/plastic which makes up the bit. Nickel is usually the worst type of metal, stainless steel is better.

thanks for your reply ! It is a racing D and definitely not too small- I can fit a finger between her lip and the D. I guess I should try and find a metal one for her.

Do you think excessive sweat or salivation could cause the sore in any way ?

People think I'm horrible and have bad hands because my horse constantly has sores on the corners of his mouth. I have tried almost every bit under the sun, rubber, copper, sweet iron, rolls, snaffles, gags, combinations, full cheeks, solid one pieces, dog bones, bit guards larger, smaller. All of them make the corners of his mouth peel and when he is feeling fresh he can get a little raw. (He pulls and tosses his head, I try to just maintain pressure) I have asked a few trainers/vets about it and I was told that my horse just has a perpetual babies mouth. He won't develop the callus's needed to help prevent this. I try to keep light hands while not letting him get away with his antics.

Sometimes it just happens for one way or another. It could have been a pinch, a quick rub, and irritation. If it doesn't keep happening I wouldn't worry too much. It happens, you have metal sitting between two pieces of soft skin, it moves around, gets pulled on and what not.

I have had her in a sweet iron D and that didnt happen, but then she was just being broke and not in much work. The sore is sort of like a split open callous.

This happened when we put Ed into a rubber mouthed pelham. I had a lesson with an instructer and she picked up straight away that his bridle had stretched and the bit was too low in his mouth, causing movement and rubbing, hence the sores.
Maybe raise the bit a little?