Infantile viscera are delicate, with a poor function to resist exogenous pathogenic factors. If improper care occurs, pathogenic wind and heat will invade the body from the skin, giving rise to internal heat of the two meridians of the heart and spleen. The interiorly accumulated heat rises to the mouth and lips, causing aphtha. Also, infants cannot control their diet. If improper feeding occurs, overtaking of fat, sweet, pungent, hot and fried foods will result in accumulation of heat in the heart and spleen.

The excessive heat goes up, bringing about burning mouth and lips and aphtha. Besides, if a pregnant mother overeats greasy food, this may cause the accumulated food to generate heat. If the heat transmits to the fetus, this may give rise to the accumulation of heat in the infantile heart and spleen; or the infant suffers from constitutional yin deficiency, or consumed yin after recovery from the illness, causing the asthenic fire to rise. All these factors may result in aphtha.