What Is Testosterone and What Does It Do?

By Amy Harris

You have probably heard of testosterone — maybe in a health class or at the gym. But what is testosterone? And what does it do in your body?

You might be surprised to learn that all humans have testosterone, both those born as females and those born as males. It might be news to you that testosterone has many vital roles in the body, not just to build big muscles or boost sex drive. With a better understanding of the importance of testosterone for your health and well-being, you can take control of your hormonal health across your lifespan.

Testosterone Is a Hormone

Testosterone is a hormone. Hormones are chemical messengers your body uses to keep itself working in tip-top shape.

Having testosterone levels that are too high or too low can have an impact on everyone’s health, regardless of their assigned sex at birth.

Testosterone is the primary sex hormone in people assigned male at birth (AMAB). Estrogen is the primary sex hormone in people assigned female at birth (AFAB), although females also have testosterone. [1]

In males, the testes make testosterone. In females, the ovaries make the most estrogen, the primary sex hormone. Ovaries also produce testosterone. Male testicles produce about 15 times as much testosterone as women’s ovaries do. [2] The female body converts most of the testosterone made by the ovaries into estradiol, a type of estrogen. [1]

The adrenal glands in both males and females also produce smaller amounts of another hormone named dehydroepiandrosterone (DHEA). The adrenal glands are triangle-shaped glands located on top of each kidney that are about the size of the top of your thumb. Your body can turn DHEA into testosterone. [1]

What Does Testosterone Do in People Assigned Female at Birth (AFAB)?

If you have ovaries, a vulva, and a vagina, testosterone impacts your health and well-being, even though your levels may be lower than those in people with a penis and testicles. In people AFAB, testosterone plays a role in [3-5]:

• Sexual development at puberty

• Keeping menstrual cycles regular

• Fertility

• Maintaining bone density and bone health

• Sexual function, including sexual desire and the ability to orgasm

• Metabolism

• Muscle mass and strength

• Mood.

In those people AFAB, testosterone levels are highest in their 20s and 30s, after which they begin to fall, slowly and steadily. [5] The signs and symptoms of low testosterone levels in women can be much more subtle than when they are too high, such as in people with polycystic ovarian syndrome (PCOS). [1]

What Does Testosterone Do in People Assigned Male at Birth (AMAB)?

Testosterone drives the development of testes (male sex organs) in babies with XY chromosomes during pregnancy. Testosterone is produced primarily in the testicles. Testosterone is the hormone that drives the body’s production of sperm. [4]

Testosterone also plays a critical role in puberty, when people start developing adult bodies. During puberty, rising testosterone levels cause [1,4]:

• Body and pubic hair growth

• An increase in height

• Enlargement of the penis, testes, and prostate gland

• Increased sex drive, called libido

• Voice changes

In adult males, testosterone continues to be important for health and well-being by [1]:

• Driving the production of red blood cells, cells in your blood that carry oxygen

• Maintaining libido (sex drive) and mood

• Keeping bones and muscles strong

It is normal for men’s testosterone levels to gradually decline with age. Healthy males will typically see a 1% decline in testosterone every year after the age of 30. [6]. Some medical conditions or situations cause men to have lower than normal testosterone levels, such as obesity, genetic disorders, or taking some cancer medications. [4]

How Do You Know if Your Testosterone Level Is Normal?

Having testosterone levels that are too high or too low can cause unpleasant symptoms for both men and women. In those people AMAB, abnormally high or low testosterone levels can cause signs and symptoms such as {1,4,7,8}:

• Mood changes, including anxiety, irritability, and depression

• Changes in sexual function, including erectile dysfunction (ED)

• Changes in hair growth, including balding

• High blood pressure

• Trouble with memory and concentrating

Some of the symptoms of abnormally high or low testosterone levels in people AFAB can include [1,4,7]:

• Infertility

• Voice changes

• Changes in body hair

• Enlargement of the clitoris, a small organ above the opening to the vagina, which is responsible for female sexual pleasure and orgasm

• Irregular periods

• Acne

• Mood changes, including anxiety, irritability, and depression

For both men and women, it’s important to have normal testosterone levels because testosterone is important for a healthy metabolism. Metabolism is how your body breaks down food into energy.

Testosterone tests can help you determine if your levels are within the normal testosterone range for your age. These tests measure either total testosterone, free testosterone, or both. [1]

What Is the Difference Between T and Free-T?

You may have heard that there are two types of testosterone: Testosterone (T) and free-testosterone (Free-T). The difference between the two really matters when testing your testosterone levels.

Most of the testosterone in both males and females travels around in the bloodstream, connected to a protein. This protein is called sex hormone-binding globulin (SHBG). It can also bind to another protein called albumin. [4]

Free testosterone is not bound to SHBG. Because it is free, it can pass more easily into cells through their outer walls, called the cell membranes. Testosterone can’t move freely through the cell membrane when bound to proteins. In order to keep the cells of your body working, testosterone needs to get inside them. [5]

To get the most accurate sense of your hormonal health, it helps to pay attention to free (unbound) testosterone. Free-T is what will cause the effects you do or don’t want, depending on your levels of Free-T.

How Do You Know if Your Testosterone Levels Are Normal and Healthy?

If you think you may have symptoms of high or low testosterone, it can be helpful to talk to a healthcare provider. They can order some tests or send you to a specialist. They can also help you make sense of your test results. Everlywell virtual care offers you access to healthcare providers via telehealth from the comfort of your home.

A blood test is used to diagnose testosterone levels that are too high or too low. Laboratory testing can be less accurate in women than in men. [5] There is no established value or level of testosterone in women used to diagnose a testosterone deficiency. [5]

The Everlywell Testosterone Test measures your free testosterone levels and can help you understand whether your symptoms might be related to having too much or too little testosterone.

Do You Need to Test Your Testosterone Before Starting Testosterone Hormone Therapy?

Yes, it is a good idea to check that your testosterone levels are normal before deciding to take additional testosterone. Testosterone therapy, sometimes called testosterone replacement therapy (TRT), means taking manufactured testosterone in the form of a medicine.[9]

In people AMAB, TRT can help treat symptoms of low testosterone. In people AFAB, there is no FDA-approved testosterone product. Some providers and consumers either use products approved for use in men or get testosterone through compounding pharmacies. [3]

Medical guidelines recommend that all people considering TRT check whether or not their testosterone levels are in the normal range. [3,5,8] If a person’s testosterone levels are already too high, it might not be safe or healthy for them to take additional testosterone. TRT can have some risks for both men and women. [3,5,7-9]

Some pre-existing health conditions could make TRT unsafe. These include: [3,5,7-9]

• Prostate cancer

• Breast cancer

• Some types of heart disease

• A history of blood clots

• Untreated obstructive sleep apnea (OSA). OSA is obstructed breathing during sleep

• Polycystic Ovarian Syndrome (PCOS)

Take Control of Your Hormonal Health With Everlywell

Now that you know the basics of what testosterone is and what it does in your body, you can see how important testosterone is to your overall health. Understanding testosterone is just one part of the puzzle that is your body’s hormonal health.

Knowing the signs and symptoms of unhealthy levels of testosterone can help you get the tests and treatments you need to start feeling better sooner. Everlywell makes it easier for you to be in the driver’s seat and take better care of yourself.