Why Does the Corner of My Mouth Keep Splitting and Getting Sore? (Angular Cheilitis)

A corner of the mouth that repeatedly splits, stings, or forms a tender crust may be related to angular cheilitis. This is inflammation where the upper and lower lips meet. It can affect one side or both sides, and the discomfort may become more noticeable when you smile, yawn, eat, or open your mouth widely.

Angular cheilitis often begins when saliva, dryness, friction, or irritation weakens the delicate skin in the mouth corners. Yeast or bacteria may then contribute to ongoing inflammation. Because several conditions can look similar, a dermatologist can evaluate persistent or recurring symptoms and help identify the likely cause.

Quick answer

• Repeated moisture from saliva can soften and irritate the skin at the corners of the mouth.
• Dryness, lip licking, dental fit, skin sensitivity, and certain health or nutritional factors may contribute.
• Yeast or bacteria can sometimes become involved after the skin barrier cracks.
• A bland protective ointment and avoiding irritation may help while the area heals.
• Persistent, worsening, or frequently recurring cracks should be evaluated by a dermatologist.

What is angular cheilitis?

Angular cheilitis is an inflammatory condition affecting one or both corners of the mouth. The skin may look red, cracked, scaly, crusted, pale, or softened from moisture. Some people notice burning, tenderness, itching, or pain when moving their lips.

It is different from a typical chapped lip because it concentrates in the folds where the lips meet. Angular cheilitis itself is generally not considered contagious, although an underlying yeast or bacterial infection may require targeted care.

Why does the corner of the mouth keep splitting?

The mouth corners are exposed to frequent movement and moisture. When saliva settles in the folds, it can evaporate and leave the skin dry and vulnerable. Once a small crack develops, speaking, eating, and facial movement can repeatedly reopen it.

Common causes or contributing factors include:

• Saliva and lip licking: Repeated wetting and drying can weaken the skin barrier.
• Dry or irritated skin: Cold weather, wind, dehydration, harsh oral-care products, and sensitive skin may contribute.
• Drooling during sleep: Saliva may collect in the mouth corners overnight.
• Dental or bite changes: Dentures, missing teeth, an altered bite, or deeper facial folds can allow moisture to pool.
• Contact irritation or allergy: Toothpaste, mouthwash, cosmetics, lip products, dental materials, or flavored products may trigger irritation.
• Yeast or bacteria: Microorganisms may grow more easily in persistently moist, cracked skin.
• Inflammatory skin conditions: Eczema or another form of dermatitis can affect the lip area.
• Nutritional or health factors: In some cases, iron or vitamin deficiencies, dry mouth, diabetes, immune conditions, or digestive disorders may be associated with recurring symptoms.

Is it angular cheilitis or a cold sore?

Angular cheilitis usually stays within the crease at the corner of the mouth and often appears as a fissure, raw patch, or crust. Cold sores more often begin with tingling and develop into grouped, fluid-filled blisters caused by the herpes simplex virus.

Appearance alone is not always enough to tell them apart. Cracks, blisters, ulcers, persistent scaling, and sores around the mouth can have several causes. Avoid sharing lip products while the cause is uncertain, and consider an evaluation if the area is blistering, spreading, or repeatedly returning.

What can you do at home?

Conservative care should focus on protecting the skin and reducing irritation:

• Apply a thin layer of plain petroleum jelly or another fragrance-free barrier ointment to clean, dry skin.
• Avoid licking, picking, rubbing, or peeling the affected area.
• Pause fragranced, flavored, plumping, or medicated lip products that may sting.
• Use a gentle toothpaste and avoid harsh mouthwash if these products seem irritating.
• Gently blot saliva from the mouth corners rather than wiping repeatedly.
• Limit foods that burn the area, such as very spicy, acidic, or salty foods, until it feels calmer.
• Keep dentures and oral appliances clean and have their fit checked when appropriate.

Avoid starting leftover antibiotic, antifungal, or steroid creams without professional guidance. The appropriate option depends on what is causing the inflammation, and some products may worsen or mask another condition.

How a dermatologist may evaluate it

A dermatologist may examine the location, appearance, duration, and pattern of recurrence. They may also ask about lip products, oral-care products, medications, dental appliances, drooling, dry mouth, skin conditions, and general health.

When infection is suspected, testing may be considered to look for yeast, bacteria, or a viral cause. Frequently recurring cases may warrant discussion of nutritional testing, underlying health factors, contact allergy, or dental fit.

Professional options

Care is based on the suspected cause. Common options may include a protective barrier, an antifungal medication, an antibiotic medication, a short course of an anti-inflammatory treatment, or changes to products that may be irritating the skin. Dental assessment may help when dentures, bite changes, or saliva pooling contribute.

Your clinician can help you decide which approach is appropriate. Treating only the visible crack without addressing moisture, irritation, dental fit, or another trigger may allow the problem to return.

When should you see a dermatologist?

Schedule an evaluation when the split does not improve with gentle barrier care, repeatedly returns, or becomes increasingly painful. Prompt assessment is also important if you notice:

• Spreading redness, warmth, swelling, pus, or significant crusting
• Grouped blisters, open ulcers, or sores in other areas of the mouth
• Bleeding that continues or a firm, thickened, or persistent spot
• Difficulty eating, drinking, or opening your mouth
• Fever or feeling generally unwell
• Unexplained fatigue, digestive symptoms, weight changes, or other signs that could suggest an underlying issue
• A weakened immune system or poorly controlled diabetes

A sore that remains in one location or does not heal should not automatically be assumed to be angular cheilitis. A dermatologist can check for other inflammatory, infectious, precancerous, or oral conditions.

Frequently asked questions

Why does the crack reopen every time I smile?

The corner of the mouth stretches whenever you smile, talk, yawn, or eat. If the skin barrier has not fully recovered, that movement can reopen the fissure. Ongoing saliva exposure or irritation can also slow healing.

Can toothpaste cause sore mouth corners?

Toothpaste ingredients, flavorings, whitening agents, and foaming agents can irritate sensitive skin in some people. A dermatologist may recommend simplifying your oral-care products if contact irritation is suspected.

Is angular cheilitis caused by a vitamin deficiency?

Low iron or certain vitamin levels can be associated with angular cheilitis, but they are not the cause in every case. Testing is most useful when symptoms recur or when other signs suggest a deficiency.

Can I use an antifungal cream on it?

An antifungal may help when yeast is contributing, but not every cracked mouth corner is fungal. It is better to confirm the likely cause, especially when symptoms are persistent, severe, or recurrent.

Why is only one corner affected?

One-sided irritation can occur because of sleeping position, saliva flow, dental alignment, a localized product reaction, or uneven skin folds. A persistent one-sided sore deserves evaluation to rule out other causes.

How can I reduce the chance of it returning?

Keep the mouth corners protected, avoid lip licking, simplify irritating products, manage dry mouth or drooling, and address dental fit when relevant. Recurring episodes may need a dermatologist’s evaluation to identify an underlying trigger.

This article is for educational purposes and is not medical advice. For diagnosis and personalized treatment, please book an appointment with a board-certified dermatologist.

Sources & further reading

• Cleveland Clinic – Angular Cheilitis: What it is, Symptoms, Causes & Treatments
• DermNet – Angular cheilitis image