Fluoride produces an anti-acid-etching effect on the enamel surface of milk teeth. Fluoride mainly targets the enamel of the milk teeth, so it is mainly applicable to children as well. Children have a high prevalence of caries in their milk teeth due to their dietary habits and limited ability to clean their oral hygiene, and the use of fluoride can effectively control the progression of caries. Lower pH acids cause demineralization and dissolution of the enamel columns themselves and the enamel interstices of the enamel. Continued action of the acid results in dissolution of the tooth surface accompanied by softening of the enamel and ultimately structural defects. However, sodium fluoride has been shown to be highly toxic, so it is generally not allowed to be added to toothpaste or only allowed to be added in small amounts. Sodium fluoride is also used as an insecticide in agriculture, a fungicide in the brewing industry, and a preservative in medicine.