That painful split or crack at the corner of your mouth is almost certainly angular cheilitis, one of the most common skin conditions affecting the lips. It happens when moisture gets trapped in the skin folds at the corners of your mouth, softening the skin until it breaks down and cracks. Once the skin is compromised, fungal or bacterial organisms move in and make it worse. The good news: it’s very treatable, and understanding the cause helps you stop it from coming back.
How the Crack Forms
The corners of your mouth are uniquely vulnerable. Saliva naturally pools there, and unlike the rest of your lip, the skin at the corners folds over itself slightly. When saliva sits in that fold, it softens and weakens the outer layer of skin, a process called maceration. As the skin dries, it tightens and splits. Every time you open your mouth to eat, talk, or yawn, the crack reopens.
Once the skin is broken, a yeast called Candida (the same organism behind oral thrush) often colonizes the wound. Bacteria can join in too. This creates an infection cycle: the crack stays inflamed, which keeps it moist, which feeds the organisms, which prevents healing. That’s why these sores can linger for weeks if you don’t actively break the cycle.
The Most Common Causes
Several things can set this process in motion, and more than one may apply to you at the same time.
Lip licking and dry weather. Habitually licking your lips feels soothing in the moment, but saliva evaporates quickly and strips away natural oils. In cold or dry climates, the skin at the corners dries out even faster, making cracks more likely. Sleeping with your mouth open or drooling at night has the same effect.
Nutritional deficiencies. This is a bigger factor than most people realize. Nutritional deficiencies account for roughly 25% of all angular cheilitis cases. The key nutrients involved are iron, riboflavin (B2), niacin (B3), pyridoxine (B6), and cobalamin (B12). If your diet is limited, you’ve been unusually fatigued, or you have heavy periods (a common cause of iron loss), a deficiency could be the underlying trigger. A simple blood test can rule this in or out.
Dental appliances and bite issues. Dentures that don’t fit properly are a classic cause, especially in older adults, because they change how the lips sit and can create deeper folds at the corners where saliva collects. Braces, retainers, and headgear can have a similar effect. Misaligned teeth or an overbite can also alter the resting position of your lips enough to trap moisture.
Skin changes with age. As skin loses elasticity, the folds at the mouth corners deepen. Deeper folds hold more moisture. This is why angular cheilitis becomes increasingly common in older adults, especially those who wear dentures.
Weakened immune function. Conditions that suppress your immune system, including diabetes, inflammatory bowel disease, and HIV, make it harder for your body to fight off the Candida yeast that colonizes these cracks. If you’re getting angular cheilitis repeatedly and can’t identify an obvious external cause, it’s worth having bloodwork done to check for an underlying condition.
Angular Cheilitis vs. Cold Sores
People often confuse the two, but they’re different conditions with different causes. Cold sores are caused by the herpes simplex virus and typically appear on the lip itself, not in the corner. They start as a cluster of tiny fluid-filled blisters that eventually burst, crust over, and heal. Angular cheilitis looks more like a single crack or split, often with redness and some crusting, but without the blistering stage. Cold sores also tend to tingle or burn before they appear, while angular cheilitis usually just feels raw and sore, especially when you open your mouth wide.
The treatments are completely different too. Antiviral medications work on cold sores but do nothing for angular cheilitis, and vice versa. If you’re not sure which you’re dealing with, the location is your best clue: right in the corner of the mouth, where the upper and lower lip meet, points strongly toward angular cheilitis.
How to Treat It
The standard approach combines three things: an antifungal to kill the Candida yeast, a mild anti-inflammatory to bring down the redness and swelling, and a barrier ointment to protect the skin from further saliva exposure. Your doctor or dentist can prescribe the antifungal and anti-inflammatory as topical creams. Between applications, an unflavored petroleum-based ointment (plain Vaseline works) soothes the area and creates a physical barrier that keeps saliva from re-saturating the skin.
Most cases clear up within one to two weeks with consistent treatment. The key mistake people make is stopping too early. If you quit the antifungal as soon as the crack looks better but the yeast hasn’t been fully eliminated, it comes right back.
For mild cases that just started, you can try the barrier ointment alone. Apply a thick layer of petroleum jelly to the corners of your mouth before bed and throughout the day. If there’s no improvement within a few days, or if the area is very red, swollen, or oozing, you likely need the antifungal component.
Preventing It From Coming Back
Angular cheilitis is notorious for recurring, especially if the underlying cause hasn’t been addressed. The most effective prevention strategies target the specific trigger:
- Keep the corners dry and protected. Apply petroleum jelly or a thick lip balm (unflavored, without irritants like menthol or camphor) to the mouth corners before sleeping and during the day in dry weather. This prevents saliva from softening the skin.
- Stop licking your lips. This is easier said than done, but it’s often the single biggest factor. The ointment barrier helps here too, since it gives your tongue something unpleasant to encounter.
- Check your nutrition. If you eat a limited diet, consider whether you’re getting enough iron, B2 (found in dairy, eggs, and leafy greens), and B12 (found in meat, fish, and fortified foods). A multivitamin can fill gaps, but a blood test is the most direct way to identify a deficiency.
- Get dental work checked. If you wear dentures, have them evaluated for fit. Ill-fitting dentures are one of the most correctable causes. Misaligned teeth or bite issues may improve with orthodontic treatment like braces or retainers.
If you’re doing everything right and the cracks keep returning every few weeks, that pattern itself is useful information. Recurrent angular cheilitis that resists straightforward treatment often signals something systemic, whether that’s an undiagnosed nutritional deficiency, diabetes, or another condition affecting immune function. A doctor can run targeted bloodwork to find out what’s driving it.