How does cleft lip occur? Are cases of cleft lip more common in some countries than others? Why is this?

Cleft lip is a birth defect in which the upper lip does not form properly. It can range from a small notch in the lip to a complete split in the lip and palate. Cleft lip occurs when the tissue that forms the lips fails to fuse properly during fetal development. The exact cause of cleft lip is unknown, but it is thought to be due to a combination of genetic and environmental factors. Cleft lip is more common in certain countries, such as China and India, than others. This may be due to genetic factors, as well as environmental conditions during pregnancy, such as malnutrition or exposure to certain toxins. Additionally, cleft lip is more common in males than females. Treatment for cleft lip typically involves surgery to repair the defect. In some cases, additional surgeries may be required to correct related defects or improve appearance. With proper treatment, most people with cleft lip can lead normal, healthy lives.