Testosterone is the primary sex hormone in males, but it is also important in females. Testosterone is secreted from the testicles in males, and from the ovaries in females.
Testosterone has an important role during the life cycle of both males and females. Testosterone levels before birth are associated with sex formation, potentially brain masculinization during early infancy, and pubertal effects, including penis or clitoris enlargement, increased libido, remodelling of facial bones, acne, pubic hair, and deepening of voice.
In adult males, testosterone is necessary for normal sperm development, enhances muscle growth, and regulates platelet aggregation. In females, testosterone also enhances muscle and bone growth, may modulate the physiology of vaginal tissue, and contributes to female genital sexual arousal.
In healthy women, testosterone briefly increases mid menstrual cycle to coincide with ovulation and the most fertile period of the cycle. Testosterone helps to promote the development of follicles, which hold and release eggs during ovulation. The correct level of testosterone is important, as both too much or too little can interfere with female fertility.
The signs of reduced testosterone include low muscle mass, poor sleep, lack of energy, depression, low libido, and vaginal dryness. Excess testosterone can lead to acne, polycystic ovary syndrome, irregular menstruation, increased body hair, and low HDL (good) cholesterol.