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Health

Young/prime adulthood can be considered the healthiest time of life and young adults are generally in good health, subject neither to disease nor the problems of senescence. Strength and physical performance reach their peak from 18 to 39 years of age. Flexibility may decrease with age throughout adulthood.

The female reproductive system reaches its peak fertility during the early 20s.

Of women who want to become pregnant,

As teens transition into young adulthood, engagement in risky behavior may be noticeable, which may result in health risks such as "unintended injury, unprotected sex, violence, binge drinking, motor vehicle incidents, suicide, and poor diet and nutrition." In developed countries, mortality rates for the 18–40 age group are typically very low. Men are more likely to die at this age than women, particularly in the 18–25 group: reasons include car accidents and suicide. Mortality statistics among men and women level off during the late twenties and thirties, due in part to good health and less risk-taking behavior.

Regarding disease, cancer is much less common in young than in older adults. Exceptions are testicular cancer, cervical cancer, and Hodgkin's lymphoma.

In sub-Saharan Africa, HIV / AIDS has hit the early adult population particularly hard. According to a United Nations report, AIDS has significantly increased mortality of between ages 20 to 55 for African males and 20 to 45 for African females, reducing the life expectancy in South Africa by 18 years and in Botswana by 34 years.