Children who share sleep with their parents are actually more independent than their peers. They perform better in school, have higher self esteem, and fewer health problems. After all, who is more likely to be well-adjusted, the child who learns that his needs will be met, or the one who is left alone for long periods of time? McKenna suggests that it is confusing for a baby to receive cuddles during the day while also being taught that the same behavior is inappropriate at night.The Commons report states that when babies are left alone to cry themselves to sleep, levels of cortisol, a stress hormone, are elevated. Commons suggests that the constant stimulation by cortisol in infancy causes physical changes in the brain. "It makes you more prone to the effects of stress, more prone to illness, including mental illness, and makes it harder to recover from illness," he concludes.