Tens of thousands of young girls around the world are missing school due to excruciating period pain — and are not seeking help — according to a recent study published in the Journal of Women’s Health.

The extensive study found that globally 71% of young women experience painful periods, with 20% of them missing classes because of the pain. 

Researchers analyzed the effects of dysmenorrhea — the clinical term for period pain — on academic performances in 21,573 young and adolescent girls. The results revealed that 20.1% of women reported absences from school or university due to period pain and 40.9% reported decreased performance or lowered concentration in classrooms. 

Researchers also found that the widespread belief that painful periods are normal and commonly experienced by all teenage girls keeps young girls from seeking medical attention for their pain and can often worsen the situation.

“This lowered classroom efficiency during the period is something women often feel they must put up with, meaning that both adolescent girls and young women may be significantly disadvantaged in their studies by the impact of period pain,” Dr. Mike Armour, a post-doctoral research fellow at the National Institute of Complementary Medicine and a co-author of the study, said in a press release. 

“This often occurs at a crucial time in their academic lives during their final schooling years when academic results can have long term consequences,” he added.

Participants also told researchers that their period pain led them to refrain from engaging in social, athletic, and school activities, or caused them to restrict their participation.

But it’s not just the pain that keeps girls out of school. In many cases, girls do not have access to menstrual hygiene products or face stigma and discrimination attached to menstruation. 

A poll conducted by the brand Always found that 1 in 5 girls in the US have missed school because of inaccessibility to period products.

Read More: Gina Rodriguez and Always Are Helping Girls Stay in School During Their Periods

In India, Nepal, and several African countries, where period stigma is still a major issue, girls of menstruating age are often denied the same resources as young boys, affecting their lives at home and in classrooms, restricting their educational and personal growth. Their opportunities may be further limited during their periods.

Around the world, girls are less likely to graduate from secondary school than boys. In fact, according to UNESCO worldwide, 131 million girls are out of school — and 100 million of those are girls of high school age. Although many underlying reasons contribute to the issue, menstruation stigma and lack of menstrual hygiene education play major roles. 

"Improving women's education about menstruation may help women make better choices about self-care and when to seek medical treatment,” Armour said.