Biology
Human Growth
Quick fact
The fastest growth in a human's life occurs before birth, but the second fastest is during the adolescent growth spurt, when some teenagers can grow over 4 inches (10 cm) in a single year.
Why this is interesting
You started as a single cell, yet you're now tall enough to reach a shelf. How does your body know when and how much to grow?
Read the full explanation
Understanding Human Growth
Human growth is not a steady, continuous process but occurs in stages with distinct patterns. From birth to about age 2, growth is rapid but decelerates. During childhood, growth is slower and steady, until a sudden acceleration called the adolescent growth spurt occurs, typically around ages 10–14 for girls and 12–16 for boys. This spurt is driven by hormones like oestrogen and testosterone, which also trigger sexual maturation. After the growth spurt, growth plates in the long bones close (ossify), and final adult height is reached. The entire process is orchestrated by the endocrine system, particularly the growth hormone (GH) from the pituitary gland and insulin-like growth factor 1 (IGF-1), along with thyroid hormones and sex steroids.
A deeper explanation
Growth is primarily regulated by the growth hormone – insulin-like growth factor axis. The hypothalamus releases GHRH (growth hormone releasing hormone) to stimulate the pituitary to secrete GH. GH acts on the liver to produce IGF-1, which then stimulates the growth of cartilage cells in the epiphyseal plates of long bones. These plates are responsible for longitudinal bone growth. The rate of growth is also modulated by nutrition, sleep, stress, and genetics. The closing of the epiphyseal plates is triggered by oestrogen in both sexes, which accelerates bone maturation and eventually stops growth. Understanding human growth matters because disruptions—from malnutrition, hormonal imbalances, or genetic conditions—can lead to short stature, gigantism, or other growth disorders. It also explains why puberty timing affects final height and why good nutrition is critical during childhood and adolescence.