When the baby’s tongue is dark, generally speaking, it is more likely that the digestive function of the gastrointestinal tract itself is disturbed, and food, infection and other factors may also cause the color of the tongue to change. Careful parents can observe that when the baby’s tongue is dark, there is often obvious bloating, constipation, nausea, loss of appetite and other phenomena that suggest the presence of gastrointestinal dysfunction. This is the time to check what foods the child has eaten recently, or even keep a diet diary with the child’s symptoms next to it to sometimes be able to find the cause. Other children are suffering from bacterial toxins that stimulate gastrointestinal dysfunction, which changes the pH of the oral saliva and makes the tongue easily stained and turn black. In addition, indigestion, stress and other conditions that affect the body’s immunity may also cause the growth of mycobacteria and the appearance of a black tongue. Some children are taking Chinese medicine and the medication may cause a change in the color of the tongue moss. In conclusion, there are many reasons that can cause a black tongue, which is a sign of an organism disease and we need to actively diagnose and treat it, but at the same time, the change and fading of the tongue color is never instantaneous in a day or two, and requires continuous observation.