It is impossible for a child to have double eyelids if both parents have single eyelids. Whether a child has double eyelids or not is mainly related to the parents’ genetic chromosomes, as follows. In genetic medicine, double eyelids are dominant and single eyelids are recessive. If both parents have double eyelids and both parents have a dominant gene, the heritability of double eyelids is 100% regardless of the combination; however, if one parent has a recessive gene, the heritability of double eyelids in the child is still 100%, but the child may have a recessive gene for single eyelids. If both parents have a recessive gene, the child’s heritability of double eyelids is 75%, and the probability of single eyelids is 25%; if both parents have single eyelids, the child’s genetic pattern has only one possibility, which is all recessive, i.e., single eyelids.