Cracks in the corners of your mouth are almost always a condition called angular cheilitis, and the most common cause is a fungal or bacterial infection triggered by excess moisture collecting in the skin folds at the lip corners. The condition looks like red, raw, split skin right where your upper and lower lips meet, and it can affect one or both sides. While infection is the immediate culprit in most cases, several underlying factors set the stage for it.
Infection Is the Primary Cause
The cracked, irritated skin at the mouth corners is typically colonized by yeast (most often Candida, the same fungus behind oral thrush) or by bacteria like Staphylococcus. In many cases, both organisms are present at the same time. The corner of the mouth is a natural trap for saliva, and that warm, moist environment is exactly where these microbes thrive. Once the skin stays damp long enough, it softens and breaks down, creating small fissures that deepen into painful cracks.
This is why treatment usually starts with a topical antifungal cream applied to the corners of the mouth, often combined with a mild anti-inflammatory to calm the redness and swelling. A two-week course is standard. But getting rid of the infection only solves the immediate problem. If whatever caused the moisture buildup in the first place isn’t addressed, the cracks tend to come back.
Saliva Pooling and Lip Licking
Anything that keeps the corners of your mouth wet increases your risk. The most straightforward example is habitual lip licking. When you lick your lips, saliva briefly moistens the skin, then evaporates and leaves it drier than before. Your body responds by licking again, and the cycle accelerates. Saliva also contains digestive enzymes that irritate delicate skin, so the corners of the mouth get a double hit: constant dampness plus chemical irritation.
Drooling during sleep has the same effect. If you sleep with your mouth open or on your side, saliva can pool at the lip corners for hours. People who breathe through their mouth, whether from nasal congestion, a deviated septum, or habit, are especially prone to this. Cold, dry, windy weather worsens everything because it dries out the lip surface, prompting more licking.
Dentures and Changes in Facial Structure
Poorly fitting dentures are one of the most common causes of angular cheilitis in older adults. When dentures don’t maintain the proper vertical height of the face, the lower third of the face effectively shortens. This creates deeper skin folds at the mouth corners, forming pockets where saliva collects and sits. Even well-fitting dentures can harbor Candida if they aren’t cleaned thoroughly, seeding the mouth corners with yeast every day.
The same principle applies to anyone who has lost teeth without replacing them, or whose natural bite has changed enough to deepen the creases around the mouth. Age-related loss of skin elasticity and facial volume can have a similar effect, which is why angular cheilitis is more common in older people even without dentures.
Nutritional Deficiencies
When cracked mouth corners keep coming back or don’t respond well to antifungal treatment, a nutritional deficiency may be part of the picture. The vitamins and minerals most strongly linked to angular cheilitis are:
- Iron: Low iron impairs immune function and slows tissue repair. Iron deficiency anemia is one of the classic systemic causes of recurrent mouth corner cracks.
- B vitamins: Riboflavin (B2), niacin (B3), pyridoxine (B6), and folate (B9) all play roles in maintaining healthy skin and mucous membranes. Deficiency in any of them can make the lip corners more fragile and prone to splitting.
- Zinc: Zinc supports wound healing and immune defense. Low zinc levels make it harder for cracked skin to repair itself and easier for infections to take hold.
These deficiencies can result from a restricted diet, digestive conditions that impair nutrient absorption (like celiac disease or Crohn’s disease), heavy menstrual periods, or chronic illness. If your mouth corners crack repeatedly despite good hygiene and moisturizing, a blood test to check your iron, zinc, and B vitamin levels is worth requesting.
Underlying Health Conditions
Certain medical conditions make angular cheilitis more likely by weakening the immune system or altering the balance of microbes in and around the mouth. Diabetes is a significant one: elevated blood sugar feeds yeast growth and impairs the body’s ability to fight off minor skin infections. People with diabetes are more prone to Candida overgrowth throughout the body, and the mouth corners are a common site.
Inflammatory bowel disease, particularly Crohn’s disease, can cause angular cheilitis both through nutrient malabsorption and as a direct oral manifestation of the disease. Immune-suppressing conditions, including HIV and the use of immunosuppressive medications like corticosteroids or chemotherapy, also raise risk. Even a course of oral antibiotics can trigger angular cheilitis by disrupting the normal bacterial balance in the mouth and allowing yeast to overgrow.
How to Tell It Apart From a Cold Sore
Angular cheilitis and cold sores (herpes simplex) can look similar at a glance, but they behave differently. Cold sores typically start with a tingling or burning sensation before any visible change, then erupt as clusters of small fluid-filled blisters that crust over. They can appear anywhere around the mouth and nostrils, not just at the corners.
Angular cheilitis, by contrast, stays confined to the corners of the mouth. It shows up as redness, cracking, and sometimes shallow erosions rather than blisters. There’s soreness and tightness, especially when you open your mouth wide, but no tingling prodrome. If you see distinct blisters appearing in crops, that points more toward herpes. If you see raw, fissured skin isolated to one or both lip corners, angular cheilitis is far more likely.
What Helps and What to Avoid
The single most effective thing you can do at home is keep the corners of your mouth dry and protected. A thin layer of petroleum jelly or a zinc oxide barrier cream creates a physical shield that blocks saliva from sitting on the skin. Apply it before bed and throughout the day, especially before eating. This doesn’t treat an active infection, but it breaks the moisture cycle that caused the problem and prevents recurrence once the infection clears.
Avoid licking your lips, even when they feel dry. Use a plain, fragrance-free lip balm on the lip surface itself, and reserve the barrier ointment for the corners specifically. If you wear dentures, have the fit evaluated. Clean dentures nightly with a denture-soaking solution rather than just rinsing with water, since Candida forms a stubborn biofilm on acrylic surfaces.
For an active infection with visible redness and cracking, over-the-counter antifungal creams designed for skin yeast infections can help. If the cracks are persistent, worsening, or keep returning after treatment, that’s a signal to look deeper for nutritional gaps or an underlying condition driving the cycle.