The most frequent sign of Gilbert syndrome is an occasional yellowish tinge of the skin and the whites of the eyes as a result of slightly higher levels of bilirubin in the blood. In people with Gilbert syndrome, bilirubin levels may increase due to: 
Illness, such as a cold or the flu
Fasting or eating a very low-calorie diet
Dehydration
Menstruation
Strenuous exercise
Stress
