Adolescence is fraught, no matter where you go through it, but social factors may make it even harder for girls. That's the message of "Growing Up Unequal," a new WHO report on gender differences based on surveys of over 200,000 teens and pre-teens.For the study, researchers looked at boys and girls ages 11, 13, and 15 in 44 countries across Europe and North America (excluding the U.S.) between September 2013 and June 2014. The findings reveal that overall, girls report lower well-being than boys, with 15-year-old girls in Britain, France, and Poland most likely to report poor health, decreasing well-being, and declining body satisfaction. That's despite the fact that levels of obesity remained the same over the duration of the study. In fact, across ages, being female was a better predictor for poor body image and dieting than BMI or family affluence. Yikes.As the study's authors point out, "Boys' bodies change in the desired direction, becoming more muscular and strong, while girls lose their so-called ideal appearance through gaining body fat." Teen boys are more likely to fight, get injured, smoke, and drink than teen girls, although the gender gap in tobacco and alcohol use is narrowing in many countries.The report acknowledges that we have a lot of work to do to ensure that girls grow up as healthy and happy as their male peers, particularly around body image, and recommends mental health programs tailored to young woman for "strengthening their self-esteem and preventing them from developing negative ideas about their bodies."When we wait until adulthood to address these issues, much of the damage has already been done — and no matter where they grow up, girls deserve better.