A split lip has many possible causes, including the following:

Picking or licking

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The skin of the lips is sensitive and easy to irritate through constant touching. People who frequently lick, bite, or pick at their lips may cause the skin to crack.

This irritation can make the person want to soothe the lips by touching or licking the area again. This behavior can lead to a cycle of dry, chapped lips.

Breaking the habit by using lip balm to soothe the lips can allow them to heal.

Weather

Chapped lips also result from other sources of irritation, such as cold or dry air or too much wind.

Changes in the weather may also lead to cuts in the corners of the lips. A split in this part of the lips can cause a burning sensation and may make even simple actions, such as smiling or chewing, painful because they stretch the sore area.

Injury

Injuries are another common cause of a split lip. These may be more likely in people who engage in contact sports, such as football or hockey, though anyone can sustain an injury.

Other injuries that can cause a split lip include:

• getting hit in the mouth
• getting a papercut on the lip
• biting the lip

Allergic reactions

The skin on the lips may react to one or more ingredients in certain products, especially those that touch the lips or mouth, such as:

• toothpaste
• dental floss
• lip balm
• lipstick
• makeup
• moisturizers
• braces

Researchers note that these allergens are responsible for 22–34% of cheilitis cases.

Anyone who notices symptoms such as inflammation, dryness, or redness after using a new lip product should stop using it.

If the symptoms persist, the person can speak to a dermatologist, who may be able to test for certain skin allergies and help the person avoid the products likely to trigger symptoms.

Sun damage

The sun may also damage the sensitive skin on the lips and lead to a split lip, although this generally only occurs after prolonged exposure.

Spending long hours under the sun without protection for the lips may lead to inflammation, which could cause pain, dryness, or cracking.

Dehydration

The body uses water to keep the skin hydrated. If a person does not have enough liquid in their body, they may start to notice changes in their skin, such as dryness or cracking.

Mild symptoms of dehydration, such as cracked lips, may appear if a person regularly does not drink enough fluids throughout the day.

Dehydration can also occur after an illness that causes high fever, diarrhea, or vomiting. These symptoms can make the body use or lose a lot of water, leading to dehydration.

Vitamin deficiencies

Although it is not as common as other causes, a vitamin or mineral deficiency may be responsible for some cases of a split lip.

Research from 2013 notes that a deficiency in certain B vitamins or iron may cause symptoms in the mouth, such as a split lip and inflammation.

Most of the time, a split lip will heal on its own with time. It is best to avoid licking the lips or picking at them during the healing process.

People can also try home remedies to speed up healing, including:

Salt water

Salt water can help keep the wound clean as it heals. Add a tablespoon of salt to a small cup of warm water. Soak a cotton swab or cotton ball in the liquid and hold it on the split lip.

Doing this may sting a little as the solution hits the open cut, but the pain should go away after a few minutes.

Baking soda paste

A baking soda poultice may also help reduce symptoms such as pain or swelling. To make this anti-inflammatory concoction, mix a tablespoon of baking soda with just enough water to form a paste — usually about a teaspoon.

Apply this paste to the lip. Allow it to sit for a few minutes before rinsing the paste away with cold water. Repeat the process every few hours if necessary.

Cold compress

Applying a cloth wrapped ice pack to the affected area may numb the pain and reduce swelling, helping the person find relief.

Only apply the ice pack for about 10–15 minutes at a time.

Some of the steps that a person can take to promote healing can also help prevent future split lips. These steps include:

• avoiding licking or picking at sensitive lips
• wearing lip protection when out in the elements, especially in cold weather
• avoiding irritating foods, such as citrus or spicy foods
• drinking plenty of water

Some split lips can lead to an infection, which may not heal with simple home remedies.

Doctors can recommend medicated ointments or moisturizers that contain an antibacterial ingredient to help kill bacteria and protect the cut as it heals.

If the split is due to an injury, it may be larger and need medical treatment, such as stitches.

A person should also see a doctor if the split lip causes bleeding that recurs or is difficult to control or if there are signs of infection, such as swelling, redness, oozing pus, and inflammation.

A split lip is a common but potentially bothersome injury. The cut may be minor, but it can take time to heal, as people typically move their lips and mouth a lot each day.

In most cases, a split lip will generally respond well to home remedies. People experiencing persistent bleeding or signs of infection should see a doctor.