A split lip has many possible causes, including the following:
Picking or licking
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.
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.
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
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:
- dental floss
- lip balm
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.
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.
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.
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.
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