What causes dark hair to grow around a 16 yr old females belly button?

Dark hair growing around a 16-year-old female's belly button is most likely due to hormonal changes associated with puberty. During this time, increased levels of androgens (male hormones) can stimulate hair growth in areas that are typically not covered in hair, such as the belly button. This is a normal part of development and should not be a cause for concern. However, if the hair growth is excessive or bothersome, it can be discussed with a healthcare professional for potential treatment options.