An Overview of Testosterone: Function, Levels, and More

Testosterone is a sex hormone in males and females. The adrenal glands secrete it, along with the testes in males and the ovaries in females.  In males, testosterone forms reproductive organs and characteristics such as increased muscle and bone mass and body hair growth. In females, testosterone contributes to the sex drive and plays a role in the menstrual cycle. 

This article explores the hormone testosterone, its role in the body, and what happens when testosterone levels are out of balance.

Testosterone is a sex hormone present in greater amounts in males. Hormones are chemicals made by the body’s glands that circulate in the bloodstream and control certain processes.

In males, testosterone plays a key role in developing sex organs such as the prostate and testicles. It also produces other male characteristics, such as:

• male hair growth patterns on the underarms, face, and pubic area 
• deepening of the voice during puberty
• increased muscle growth
• sperm production
• growth spurts
• sex drive
• mood

Although people often think of testosterone as a male hormone, it’s also essential in the female body. In females, testosterone plays a role in the sex drive or libido.

Other characteristics that testosterone influences in females include:

• bone density
• energy
• cardiovascular functioning
• the ability to think

Testosterone levels typically change during your lifetime and even throughout the day. Levels also differ between males and females. Doctors measure testosterone levels in nanograms (ng) per decilitre (dL). 

Below are typical testosterone levels for male children and adults by age range.

Below are typical testosterone levels for female children and adults by age range.

Several conditions may cause testosterone levels to become out of balance, leading to reproductive dysfunction and other symptoms. 

Hypogonadism refers to low levels of testosterone in males. Primary hypogonadism happens when the testicles do not produce enough testosterone.

This condition may develop due to Klinefelter syndrome, in which a male is born with an extra X chromosome. Other causes of primary hypogonadism include chemotherapy and aging. 

Secondary hypogonadism happens when your pituitary gland or hypothalamus does not function correctly. Factors that may cause this include HIV, obesity, and pituitary disorders. 

Turner syndrome occurs when a female is born with only one X chromosome rather than two. This results in lower testosterone levels and a wide range of symptoms. 

Polycystic ovary syndrome (PCOS) is a common condition in which females can have elevated testosterone levels. While the exact cause of PCOS is not known, it tends to run in families.

Misusing steroids and other appearance performance-enhancing drugs (APEDs) can cause an increase in testosterone levels. This can cause hormonal problems and can put you at a higher risk for:

• heart attacks
• stroke
• blood clots
• testicular cancer
• decreased sperm production
• baldness
• tendon injury

You may notice symptoms of your testosterone level being too high or too low.

Males with low levels of testosterone may experience:

• reduced sexual desire
• decreased spontaneous erections
• loss of pubic hair
• shrinking testicles
• hot flashes
• depressed mood
• poor concentration
• increased body fat
• decreased physical performance
• reduced muscle mass

Females with low levels of testosterone may experience:

• shorter than average height
• underdeveloped ovaries
• thick neck tissue
• swelling of the neck
• heart conditions
• kidney abnormalities
• underdeveloped breast tissue
• irregular periods
• infertility

High levels of testosterone that do not result from synthetic supplementation are rare in males. In many cases, there are few observable symptoms.

Females with high levels of testosterone may experience symptoms such as:

• irregular periods or no periods
• trouble getting pregnant
• excessive hair growth on the face, chest, back, or buttocks
• thinning hair
• oily skin or acne

Medical professionals will test for low testosterone only if you have clinical symptoms such as loss of body hair, sexual dysfunction, hot flashes, or increased breast tissue in males. 

If your medical professional believes there may be an imbalance in your testosterone level, they can order a total serum testosterone lab test. To complete this test, you will need to have your blood drawn between 8–10 a.m.

If your lab results are low, you will need to repeat the test another day. During that test, your doctor may measure other hormone levels as well. 

In some cases, a brain MRI can show whether there is a problem with your pituitary gland that may be causing low testosterone levels. 

In cases where the cause of low testosterone levels is hypogonadism, your medical professional may prescribe testosterone replacement therapy (TRT).

Females sometimes take TRT to treat postmenopausal loss of sexual drive or to produce male characteristics when making a gender transition. 

Potential benefits of TRT include:

• increased sexual drive
• improved sexual function
• improved mood
• increased muscle mass
• increased bone density

Potential risks include cardiovascular complications.

Learn more about TRT.

Testosterone is a sex hormone responsible for forming many male sexual characteristics and reproductive organs. In females, testosterone contributes to the menstrual cycle and sex drive.

Low testosterone levels in males, a condition called hypogonadism, may produce many symptoms. These may include reduced sexual desire and hot flashes. Some people may also experience changes in hair volume, testicular size, and bone density. 

High levels of testosterone in males typically result from anabolic steroid use. High levels of testosterone in females generally result from an underlying medical condition.

Contact your doctor if you think your testosterone levels may be imbalanced.