A survey on sexual behaviour in the US has revealed that while Americans enjoy sex well into old age, it is only the teens who use condoms during sexual activity.
Most teens don't have sex, but when they do, condom use has become "normative" behavior, found the study, published in a special edition of the Journal of Sexual Health.
Teenage boys reported using a condom use 79 percent of the time during the last 10 times they had intercourse with a girl, while teen girls reported using a condom 58 percent of those encounters, the study found.
But condom use declines with age, and by the time people reach 50, only one in five men and one in four women uses a condom, the study found.
The data was compiled by researchers at the University of Indiana, who documented the sexual experiences and condom use -- or not -- of 5,865 Americans aged 14 to 94.
The drop in condom use is not due to a lack of sexual activity among older Americans, because Americans are sexually active "well into old age (80+)", according to the study, which was funded by a condom maker.
"But freed from concerns about contraception by virtue of age, they remain unclear or unaware about the need to continue protecting themselves and their partners from STIs," or sexually transmitted infections, it said.
The study followed a ground-breaking survey published 60 years ago by Dr Alfred Kinsey, also of the University of Indiana, and another study with nationwide reach which was published in 1994.
"This survey is one of the most expansive nationally representative studies of sexual behavior and condom use ever conducted, given the 80-year span of ages," said Michael Reece, director of the Center for Sexual Health Promotion, and one of the authors of the new research.
"These data about sexual behaviors and condom use in contemporary America are critically needed by medical and public health professionals who are on the frontline, addressing issues such as HIV, sexually transmissible infections and unintended pregnancy," he said.