Sept 23 was the International Day of Sign Languages (手语). According to the United Nations, there are about 72 million (百万) people around the world who cannot hear. They use more than 300 different sign languages. A report by the World Health Organization says that about 90 million people may have serious hearing loss (听力受损) by 2050. And 1.1 billion (十亿) young people (aged 12 to 35) may have hearing loss. This is mainly because they listen to too much loud music.