The bilirrubina comes from the degradation of another pigment, the hemoglobin, which the red globules keep in his interior and that is necessary for the oxygenation of the textiles. When the red globules break for any motive, the hemoglobin is liberated and turns in bilirrubina. Once the hemoglobin has turned in bilirrubina, this one comes to the liver, conjugates with an acid that makes her more soluble, and is eliminated this way by the biliary vesicle, in the shape of bile, to the intestine (where it serves as help in the digestion process).

The jaundice in newborn babies appears on the first day of life in almost every newborn baby and yields alone in the first days. If it is not like that, one of the treatments used in the jaundice neonatal physiological or "normal" is the exhibition of the newborn baby to visible light, well in the bogey of the blue, or to white light of wide bogey.

The light turns the bilirrubina into isomers (forms of the molecule) more soluble, that are eliminated quickly by the liver without need to conjugate with an acid, like the normal bilirrubina.

Since many biological effects take place for the exhibition to the brilliant light, the phototherapy must only be used when it is indicated specially (bilirrubina in blood near to 3-4 mg/dL and exclusion of problem of biliary routes). And the beams must always filter ultraviolet by means of a screen of crystal or Plexiglas, as well as protect the eyes of the child.