In its latest poll, which covers the 2023 academic year, the association found that girls in the same age group were similarly cautious, with 27.5% saying they had experienced their first kiss, compared with 22.8% among boys – down 13.6 percentage points and 11.1 points since 2017.

The proportion of senior high school students – aged 15-18 – who had kissed for the first time has been declining since its 2005 peak, when one in two said they had locked lips.

The latest survey, the association’s ninth in half a century, showed a lower percentage of affirmative answers to the kissing question than in the 2017 poll across all the surveyed age groups, which also sought responses from junior high school and university students, according to the Mainichi Shimbun.

The association, which surveyed more than 12,500 students, said 12% of junior and senior high school students said they had had sexual intercourse, as did 14.8% of girls – down 3.5 percentage points and 5.3 points, respectively.

But a different trend emerged when the subject turned to solitary sexual habits, with rising proportions of students in all three groups saying they masturbated.

The association partly attributed the downward trend in kissing and intercourse to the Covid-19 pandemic, which triggered school closures and official advice to avoid the “three Cs”: confined spaces, crowded places and close-contact settings.

“Limited contact with others during the coronavirus outbreak may have lowered the rate of sexual activity among junior and senior high school students,” it said.

Yusuke Hayashi, a sociology professor at Musashi University who analysed the results, said the combination of school closures and restrictions on face-to-face contact during the pandemic came “at a sensitive time, when junior and senior high school students are beginning to become interested in their sexuality”.

Hayashi told the Mainichi that the greater prevalence of masturbation “may be due to increased exposure to [sexual imagery] in manga and other media, rather than as a substitute for interpersonal sexual behaviour”.

Tamaki Kawasaki, a columnist and sociology lecturer, said the survey’s findings suggested that young Japanese were “uniformly disengaging” from sex post-pandemic.

“It shows that the trend is for people to move away from real, physical sexual activity, even at a time when it’s natural for them to be sexually active,” Kawasaki wrote in the online edition of President magazine.

“Instead, there is a stronger tendency for them to stay home and watch sexual content alone. If teens, who represent the country’s future, continue like this then it is hard to see any improvement in the declining birthrate.”