Yes, you can apply Rexidin on the tongue for the treatment of mouth ulcers. Mouth blisters are small sores that can occur on the tongue, which irritate while eating, sipping, and even speaking. Rexidin M Forte Gel suppresses the substances within our brain that cause discomfort as well as irritation. As a result, it reduces pain, stiffness, and inflammatory signs, including redness or puffiness caused by mouth ulcers.