Question: why do boys voices get deeper?

Christina Pagel answered on 26 Jun 2013:

As boys go through puberty their bodies make more testosterone – this is a hormone that produces a lot of ‘male’ traits, such as stronger muscles, facial hair, baldness (when you’re older!) and it’s also reponsible for making men’s voices deeper…

Testosterone works by lengthening the vocal cords in boys, which changes how the sound is produced.