Usually nail biting in 12 year olds is not normal and may be related to bad habits, lack of micronutrients and so on. Nail biting in a 12-year-old child may simply be a bad habit that needs to be corrected in time to develop good living habits and so on. In addition, if the child is partial to picky eating, unbalanced nutrition, lack of certain trace elements such as zinc, iron, etc., the child will also like to bite their nails, and should go to the hospital for analysis of trace elements. 12-year-old children biting nails may also be related to localized diseases of the nails, or psychological problems, nail biting fetish. Parents need to pay attention to it in time. Nail biting in 12-year-old children is generally abnormal, and may also be related to other factors. Parents are advised to bring their children to the child health care department of the hospital and follow the doctor’s instructions if necessary.