“Harelip” is an outdated term for what is now called a cleft lip, a birth defect where the upper lip doesn’t fully form during pregnancy, leaving a gap or split. The term references the split upper lip of a hare and has been considered offensive in medical circles since at least 1922, when the American Medical Association called for abandoning it. Today, the accepted terms are cleft lip and cleft palate. About 1 in every 1,000 babies in the United States is born with a cleft lip, with or without a cleft palate.
Why the Term Is Considered Offensive
The word “harelip” compares a person’s face to an animal’s, which contributes to stigma around the condition. The Cleft Lip and Palate Association advises against using it unless the person with the condition chooses to describe themselves that way. The same problem exists in other languages: the Spanish term “labio leporino” carries the same animal comparison and is being replaced by “labio hendido” or “labio fisurado” depending on the region.
How a Cleft Lip Forms
During early pregnancy, a baby’s face develops from separate tissue segments that grow toward each other and fuse together. The upper lip forms when tissue from the middle of the face and tissue from each side meet and join. The roof of the mouth (palate) forms in a similar way, with shelf-like structures growing inward from each side and fusing along the midline. This fusion process for the palate begins around 8 weeks after conception and finishes during or after the 9th week.
When these tissues don’t fully connect, a gap remains. If the gap is in the lip, it’s a cleft lip. If it’s in the roof of the mouth, it’s a cleft palate. Many children have both.
Types of Cleft Lip
Not all cleft lips look the same. The condition ranges from barely noticeable to a wide gap extending into the nose:
- Microform cleft: The lip has a visible distortion or notch but isn’t fully separated. This is sometimes called an occult cleft.
- Incomplete cleft: The lip is split through the colored border of the lip, and the nostril on that side is often displaced downward, but a band of tissue still connects across the gap near the nose.
- Complete cleft: The lip and the base of the nose are fully separated with no connecting tissue.
A cleft can also be unilateral (on one side) or bilateral (on both sides). Bilateral clefts create two gaps in the upper lip.
Causes and Risk Factors
Most cleft lips result from a combination of genetic and environmental factors, and in many cases no single cause can be identified. About 70% of cleft lip cases are “non-syndromic,” meaning the cleft is the only birth defect present. The remaining 30% occur as part of a broader genetic syndrome. Cleft lip or palate has been found in more than 400 different syndromes, including Down syndrome, Pierre Robin sequence, and Waardenburg syndrome.
Two environmental risk factors have strong evidence behind them. Smoking during pregnancy increases the risk, as does having type 1 or type 2 diabetes before becoming pregnant. Folic acid supplementation before and during early pregnancy is widely recommended in part because of its role in preventing birth defects like these, though the exact degree of protection for clefts specifically is still being studied.
How Cleft Lip Is Detected
A cleft lip can often be spotted on a routine prenatal ultrasound starting around the 13th week of pregnancy. Three-dimensional ultrasound techniques can sometimes detect it even earlier. Cleft palate alone, without a lip cleft, is harder to see on ultrasound because the gap is inside the mouth. Some cases of cleft palate aren’t discovered until after birth.
Health Challenges Beyond Appearance
A cleft lip or palate isn’t purely cosmetic. Children born with the condition face a range of practical challenges that vary depending on whether the cleft involves just the lip, just the palate, or both.
Feeding is often the first concern. Babies with a cleft palate can’t create the suction needed for breastfeeding or standard bottle-feeding because air escapes through the gap in the roof of the mouth. Specialized bottles and nipples help, and feeding specialists typically work with families in the first days after birth.
Hearing problems are common because the muscles that open and close the tubes connecting the throat to the middle ear don’t function normally when the palate is cleft. Fluid builds up, leading to repeated ear infections and potential hearing loss if untreated. Speech can also be affected, since the palate plays a key role in directing airflow during speech. Many children need speech therapy, and some require additional surgery to improve the palate’s function. Dental issues are more frequent as well, including missing teeth, extra teeth, or teeth that come in at unusual angles near the cleft site.
Surgical Repair and Timing
Cleft lip is typically repaired with surgery when the baby is between 3 and 5 months old. The two most commonly used techniques are Millard’s rotation-advancement method and the Tennison-Randall triangular flap repair. Both aim to close the gap, reconstruct the shape of the lip and nostril, and align the lip muscles so they function properly. The choice of technique depends on the type and width of the cleft.
If a cleft palate is also present, that repair usually happens later, often between 9 and 18 months, timed to support speech development. Many children go through additional procedures as they grow, including bone grafts to fill gaps in the upper jaw, dental work, nose reshaping, and sometimes speech surgery. The full course of care can stretch from infancy into the late teens, coordinated by a team that includes surgeons, dentists, orthodontists, speech therapists, and audiologists.
With modern surgical techniques, most children who are born with a cleft lip grow up with minimal visible scarring and normal speech. The condition is one of the most successfully treated birth defects, though the process requires years of follow-up care.