The American Urology Association define low testosterone as less than 300 nanograms (ng) of the hormone per deciliter (dl) of blood. They also reported that about 2 in every 100 men have low testosterone.

Testosterone production can slow as a person ages, and many older men have symptoms of low testosterone.

The hormone has many important functions, including:

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Testosterone is a sex hormone often associated with males, though females have small amounts. If a male has a low level of testosterone, the symptoms can include erectile dysfunction, and reduced bone mass and sex drive.

Below are common signs and symptoms of low testosterone in males. Females may also experience some of the following.

1. Problems with erections

Share on Pinterest Low testosterone may cause fatigue and mood changes.

Low testosterone can make it difficult to get or maintain erections.

Testosterone stimulates the penile tissues to produce nitric oxide, which starts several reactions that result in an erection.

If levels of the hormone are too low, a man may not be able to get an erection.

The following are other factors that can cause erectile dysfunction:

2. Hair loss

Many men experience hair loss as a natural part of aging, and age-related hair loss can also affect women.

Authors of a study from 2012 found that testosterone implants supported the regrowth of hair in some women who were receiving treatment for symptoms of sex hormone deficiency.

3. Reduced bone mass

Testosterone helps to produce bone tissue and maintain bone volume.

Low testosterone can lead to a reduction in this volume, which can make the bones more susceptible to fractures.

4. Reduction in testicle size

A male with low testosterone may notice a reduction in the size of their testicles that is not related to cold temperatures.

The scrotum may also feel softer than usual.

5. Reduction in the amount of semen

Semen is the fluid that makes up the majority of male ejaculate. This type of fluid helps the sperm move toward the egg.

Testosterone helps stimulate the production of semen, and reduced levels of semen can indicate a reduction in testosterone. It can also lead to trouble with fertility.

6. Difficulty sleeping

Men with low testosterone may find it difficult to fall or stay asleep.

Many males with low testosterone also have sleep apnea. This potentially severe disorder causes a person to temporarily stop breathing, which can disrupt sleep.

7. Lowered sex drive

Men with low testosterone often experience a reduction in sex drive.

A diminishing sex drive occurs naturally with age, but when the cause is low testosterone, a man will notice a significant decrease in the desire for sex.

8. Reduced muscle mass

Testosterone plays a role in the development of muscle mass, and reduced levels of the hormone can result in a significant loss of muscle mass.

However, as low testosterone causes a decrease in mass, the function and strength of the muscles do not diminish, according to the findings of a 2016 review.

9. Hot flashes

While many people associate hot flashes with estrogen levels that fluctuate during menopause, low levels of testosterone may also cause this symptom.

10. A decrease in energy levels

Low testosterone can lead to reduced levels of energy and fatigue.

A person may feel tired, even after adequate rest, or they may develop a diminished interest in exercise or movement.

11. An increase in body fat

A reduction in testosterone can lead to an increase in body fat.

In some cases, men with a deficiency of the hormone develop gynecomastia, which causes an enlargement of the breasts.

12. Changes in mood or mood swings

Some evidence suggests that men with low levels of testosterone are likely to experience a lack of focus, irritability, and depression.