What are some home remedy for cold sores in the mouth?

Virus and Stress: Viatmin B12 or vitamin d deficiency. Take a multi-vitamin everyday, spend some time in the sun, and find ways decrease stress. Apply abreva (over the counter) cream as soon as you feel the cold sore. This will shorten (or in some cases get rid of) the cold sore.

No cure- it's herpes: More than likely it's caused by a herpes outbreak (hsv-1 typically). Drinking acidic fluids can make the situation worse; with poor dental hygiene, the burden of bacteria will allow the ulcers to fester. In certain instances, medications such as Acyclovir can help. Otherwise, the burden of oral bacterial can be tamed by the use of either listerine or a warm salt water gargle for 1min, 3 times daily.

Warm salt water: There is no cure but you might try gargling with warm salt water a few times a day. Don't swallow the salt water, spit it out when you are done. If the lesions don't go away within a few days, get them checked out by your dentist or doctor.