Finger-sucking is the involuntary sticking of fingers into the mouth and lips for sucking during infancy, some with one finger and some with two fingers. Sucking is normal as it is a child’s instinct within 1 year of age. After 1 year of age, sucking brings a pleasant sensation to the child’s oral mucosa, so some children subconsciously put their fingers in their mouths. However, as the child grows up, by the age of 2-3 years, it will decrease or disappear with the maturity of all aspects. If after 2-3 years of age the child still puts the finger in the mouth and sucks, it means that it is an unhealthy and undesirable manifestation, the main reason for which may be related to the child’s poor psychological security, a more strained relationship with the parents, or the child’s timidity. Finger-sucking can have a series of, undesirable symptoms that appear, such as the appearance of open front teeth, misalignment of teeth, etc. So if a child over 2-3 years of age still has finger sucking occurring, early intervention is recommended.