“Hairlip” (more precisely spelled “harelip”) is an outdated term for a cleft lip, a common birth difference where the upper lip doesn’t fully form during pregnancy. The term compared the appearance to a hare’s split upper lip and is now considered demeaning. The medically accurate and respectful terms are cleft lip, cleft palate, or cleft lip and palate. In the United States, about 1 in every 1,031 babies is born with some form of cleft lip.
How a Cleft Lip Forms
A cleft lip develops very early in pregnancy, around the sixth week. At that stage, separate tissues on either side of the face are growing toward the center to form the upper lip and nose. These tissues normally fuse together in the midline to create the groove between the nose and mouth (the philtrum) and the full upper lip. When the fusion doesn’t complete, a gap remains. That gap is the cleft.
The cleft can range from barely noticeable to quite significant. A microform cleft is a subtle distortion of the lip without a full separation. An incomplete cleft goes through the lip’s outer edge but leaves a small band of tissue still connecting the two sides near the nostril. A complete cleft is a full separation that extends from the lip up into the base of the nose. The cleft can appear on one side (unilateral) or both sides (bilateral) of the upper lip.
What Causes It
There’s no single cause. Cleft lip results from a combination of genetic factors and environmental influences during early pregnancy. Some cases run in families, while others appear with no family history at all. Known risk factors include maternal smoking during pregnancy, diabetes, and certain medications taken in the first trimester. In many cases, though, no clear trigger is identified. A cleft lip can also occur as part of a broader genetic syndrome, but the majority of cases are isolated, meaning the cleft is the only structural difference present.
Feeding Challenges in Newborns
One of the first practical concerns for families is feeding. A cleft in the lip or palate makes it difficult for a baby to create the suction needed for breastfeeding or standard bottle feeding. The gap between the oral and nasal cavities means the baby can’t build up negative pressure to draw milk from a nipple. Milk may flow into the nasal passages, causing choking or regurgitation.
Specialized feeding equipment helps significantly. Soft squeeze bottles, nipples with wider bases that help seal across the cleft, and nipples with enlarged openings all make feeding easier. For babies with a cleft palate, a feeding obturator (a small device placed over the roof of the mouth) can temporarily close the gap, giving the baby a surface to press the nipple against. With the right tools, most babies with cleft lip feed well and gain weight normally, though feedings often take longer than usual.
Speech and Hearing Effects
Children with cleft lip alone typically develop speech normally. When the cleft extends into the palate, however, the risk of speech and hearing difficulties rises substantially.
The palate plays a key role in directing airflow during speech. A cleft palate can cause air to escape through the nose, giving speech a nasal quality and making certain sounds hard to produce. Speech therapy is a standard part of care for these children, often beginning before age two and continuing through the school years.
Hearing is another concern. The muscles that open and close the eustachian tube (which drains fluid from the middle ear) are structurally different in children with cleft palate. The tube itself tends to be shorter, and the muscle that helps it function doesn’t insert correctly. This leads to chronic fluid buildup in the middle ear, a condition that causes temporary but recurring hearing loss. One study of children with unilateral cleft lip and palate found that 82% had a history of this type of hearing loss. Even mild hearing difficulties in early childhood can affect language development and school performance, so hearing is monitored closely from infancy.
Surgical Repair and What to Expect
Cleft lip is repaired surgically, usually in the first few months of life. The traditional guideline, sometimes called the “Rule of Tens,” sets the minimum threshold at 10 weeks of age and 10 pounds of body weight. The goal of the initial surgery is to close the gap in the lip and reconstruct the nostril on the affected side to look as symmetrical as possible.
If the palate is also cleft, that repair typically happens in a separate surgery later in the first year. Children with bilateral clefts sometimes need presurgical treatment with a device called a nasoalveolar mold, which gradually reshapes the lip and nose tissues before the operation to improve the surgical result.
The initial repair is not always the final surgery. A systematic review of revision rates found that about 21% of cleft lip patients overall undergo at least one additional lip surgery later in childhood or adolescence. For bilateral cleft lip specifically, revision rates are much higher, averaging around 79%. The most common reason for revision is scar improvement. Some children also need a bone graft to the gum line around ages 8 to 12, when adult teeth are coming in, to provide bony support that the cleft disrupted.
Long-Term Outlook
With modern surgical techniques and coordinated care, most children born with a cleft lip grow up with minimal visible scarring and normal function. Treatment typically involves a team that includes a surgeon, speech therapist, audiologist, orthodontist, and sometimes a psychologist. Care spans from infancy through the mid-teens, when facial growth is complete and any final refinements can be made.
The social and emotional side matters too. Children with visible facial differences sometimes face questions or teasing, particularly in early school years. Parents who use accurate, neutral language (cleft lip rather than “hairlip” or “harelip”) help set the tone for how others talk about the condition. Most children adapt well, especially when they have consistent support and understand their own medical history in age-appropriate terms.