Aging is biochemical and cellular damage: if you are more damaged than someone of the same chronological age, then you are physically older. This implies a shorter remaining life expectancy, but it doesn't necessarily imply that you will look older. For the purpose of close comparisons between people of a similar age, exterior appearance doesn't correlate well with the health of vital organs: "Even though most adults want to avoid looking older than their actual age, research [shows] that looking older does not necessarily point to poor health. The study found that a person needed to look at least 10 years older than their actual age before assumptions about their health could be made. ... Few people are aware that when physicians describe their patients to other physicians, they often include an assessment of whether the patient looks older than his or her actual age. This long standing medical practice assumes that people who look older than their actual age are likely to be in poor health, but our study shows this isn't always true. ... We were really surprised to find that people have to look a decade older than their actual age before it's a reliable sign that they're in poor health. It was also very interesting to discover that many people who look their age are in poor health. Doctors need to remember that even if patients look their age, we shouldn't assume that their health is fine."