Jaundice is unique to newborns and occurs in about 80% of newborns, most of them are physiological, while a small percentage of pathological jaundice has the risk of causing bilirubin encephalopathy and requires active treatment. A simple and effective way to reduce jaundice is phototherapy, so some parents give their babies sunlight to reduce jaundice, is it really effective? The principle of phototherapy is to produce isomers of bilirubin under the irradiation of blue light, from fat-soluble bilirubin to water-soluble bilirubin, which can be excreted directly from the bile or urine without the combination of the liver. Bilirubin absorbs light, with the strongest effect of 450-460nm light, while blue light has a wavelength of 425-475nm, so it is considered to be the best light source for artificial irradiation to recede yellow. Sunlight is a composite light, containing these wavelengths of light, theoretically to the baby sunlight has a slight rejuvenating effect. However, for babies under 12 months of age, sun exposure can cause harm, especially the ultraviolet rays of the sun, which can easily cause sunburn, and sun exposure cannot be dressed, so it is easy for the baby to get cold and sick, which is not worth the loss. Mild jaundice is not harmful to the baby and there is no need to treat it. Bilirubin levels in newborns after birth are a dynamic process that requires consideration of their gestational age, daytime age and the presence of high-risk factors. Sun exposure is not an effective way to reduce jaundice, and children found to be jaundiced need to be seen in a timely manner and treated under the guidance of a physician.