The appearance of the first bubble of urine in the morning is very yellow is a normal physiological phenomenon. The kidney aldosterone system has to ensure the body’s water demand during sleep, resulting in increased water recycling, and the urine produced by the kidneys will be more concentrated, so the first urine in the morning will be more yellow. However, other causes cannot be ruled out. If you find that your urine is persistently yellow, you need to consider whether there are pathological causes, such as liver damage or bile duct obstruction that causes bilirubin to rise, thus causing yellow urine. In addition to this, taking special medications such as multivitamins or riboflavin-based drugs may also cause yellow urine. In people with hemolytic jaundice, because a large number of red blood cells are destroyed, urobilinogen is also absorbed through the intestine and thus converted into bilirubin, resulting in yellow urine.