The stress hormone cortisol is stable for 30 minutes from the time an infant wakes while adults experience an immediate increase, U.S. researchers say. Study leader Melissa Bright, a psychology doctoral student at the University of Georgia Franklin College of Arts and Sciences, Janet Frick, a faculty member and director of the University of Georgia Infant Research Lab, and Douglas Granger, of Johns Hopkins School of Nursing, showed the cortisol response for infants is opposite of that in adults. Cortisol is produced in the adrenal gland and is released in response to stress. It can increase blood sugar, suppress the immune system and aid in metabolism. In adults the cortisol awakening response occurs when the hypothalamic-pituitary-adrenal axis works to release cortisol, alerting the body to stress or threats, the researchers said. The team said the study involved 32 baby-mother pairs. Nineteen of the babies were female and 13 were male, ranging in age from 7.8 to 17.4 months. The mothers were instructed to collect saliva samples using cotton swabs from inside the mouths of their infants and then themselves four times on a single day: when the infants awoke in the morning, 30-45 minutes after the baby awoke, when the baby awoke from its first nap of the day and 30-45 minutes after that. The findings were published online in the journal Developmental Psychobiology.