The harelip, including cleft lip and cleft lip and palate, is a developmental and fusion disorder of the embryo caused by heredity or external factors, which may be the influence of a variety of factors and is not necessarily a genetic disease. 1. Genetic factors. Some patients with cleft lip and cleft lip and palate can be found in their immediate family members with similar deformities, which have some relationship with heredity. 2. Nutritional factors. Vitamin deficiency during pregnancy may also lead to lip deformities. 3. Infection and injury. Injuries or some viral infections during pregnancy may also lead to malformations in the development of the embryo. 4. Tobacco and alcohol factors. The incidence of cleft lip and palate is higher if you smoke or drink heavily during pregnancy. The occurrence of cleft lip is genetically related, but not absolute, and may be the result of a number of factors acting at the same time or at different times.