If the corners of your mouth are red, you might have a condition called xerostomia, or dry mouth. Red corners of the mouth are often associated with having a dry mouth. To make the redness go away, you’ll want to increase the flow of saliva in your mouth. One way to do that is by drinking more water to stay hydrated and sucking on sugar-free candies to keep your saliva flowing. You can also chew sugarless gum, which would have the same effect as the candy. Try rubbing on some oral moisturizing gel, which you can buy at a drugstore. If you use mouthwash regularly, switch to one that’s alcohol-free, since alcohol has a drying effect. You might consider changing some of the foods you eat, such as avoiding foods with a lot of salt and dry foods like crackers. Drinks containing caffeine or alcohol can also cause your body to lose moisture, so try avoiding those to see if it helps. Smoking is another behavior that can cause a dry mouth and related symptoms.
Dry mouth is not a disease. Instead, it’s a symptom of another condition that might cause your mouth to produce less saliva. If you can treat the actual problem, you might be able to make the corners of your mouth normal again. There are several causes of xerostomia, including medications that can lower saliva levels in your mouth. Some diseases can also cause a dry mouth, including diabetes, rheumatoid arthritis, high blood pressure, human immunodeficiency virus (HIV), anemia, and cystic fibrosis. Xerostomia can also happen when you’re dehydrated, which can happen if you recently had a fever, vomiting, diarrhea, or were sweating a lot. It's also common during radiation treatment for cancers in the neck or head. You might want to talk to your dentist or doctor about your dry mouth to see what the cause might be.