Testosterone is a hormone primarily produced in the testes in males and, to a lesser extent, in the ovaries and adrenal glands in females. As an androgen, it stimulates the development of male characteristics. Testosterone plays a broad role in the body, influencing physical development, reproductive function, bone density, muscle mass, and mood regulation. Understanding the timeline of testosterone secretion provides insight into its varied effects throughout a male’s life.
Testosterone Production Before Birth
The production of testosterone in males begins even before birth. Around the seventh week of gestation, the SRY gene on the Y chromosome initiates the development of the testes. Once formed, these developing testes begin to produce testosterone.
This early surge of testosterone is fundamental for male sexual differentiation. It triggers the formation of internal male reproductive organs, such as the seminal vesicles and epididymis. Additionally, it guides the development of external genitalia, ensuring the formation of a penis and scrotum. Without this prenatal testosterone, the fetus would develop female anatomical characteristics regardless of its genetic sex.
The Infantile Testosterone Surge
Following birth, male infants experience a transient period of elevated testosterone levels, often referred to as the “mini-puberty of infancy.” This surge begins shortly after birth, peaks around one to three months of age, and then gradually declines by about six months.
It is thought to play a role in the continued programming of male reproductive tissues. It may also influence brain development, contributing to male-typical behaviors and cognitive patterns later in life. This early, temporary increase in testosterone is a distinct phase, separate from the more widely recognized hormonal changes of puberty.
The Onset of Puberty
Testosterone secretion increases significantly during puberty, marking the transition from childhood to adulthood. In males, puberty commences between ages 9 and 14.
This process is initiated by the activation of the hypothalamus-pituitary-gonadal (HPG) axis. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to produce luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH then stimulates Leydig cells in the testes to increase testosterone production.
This surge drives physical transformations, including the growth and maturation of the penis and testes, voice deepening, and the development of facial and body hair. Testosterone also promotes an increase in muscle mass, bone density, and sperm production, enabling reproductive capability.
Testosterone Through Adulthood
After the changes of puberty, testosterone secretion continues throughout adulthood, playing a role in maintaining male health. It helps sustain muscle mass, bone density, and red blood cell production, and also influences libido and overall well-being, contributing to energy levels and mood regulation.
Testosterone levels in men remain within a stable range through early and middle adulthood. However, a gradual decline in testosterone levels is a normal part of aging, sometimes called late-onset hypogonadism or andropause. Even with this decline, the HPG axis continues to regulate testosterone production, adapting to the body’s changing needs over time.