The nasal septum is a structure made of bone and cartilage that separates the nasal cavity into two nasal passages. The septum is intended to divide the left and right nasal passages equally, but up to 80% of people have a septum that is crooked. This is known as a deviated septum. A deviated septum is rare in childhood, and tends to develop during the growth of bone and cartilages within the head throughout the teenage and early adulthood stages of development. In other cases it may be caused by an injury to the nose.