Testosterone is one of the body’s most powerful hormones. In the womb, it helps direct male sexual development. When boys hit puberty, testosterone deepens their voices, stimulates facial hair and fuels muscle growth. Testosterone also helps adult men maintain muscle mass, bone density and energy.

In recent years, some conservatives have turned this common hormone into something much larger: a symbol of American masculinity itself.

Tucker Carlson and Health and Human Services Secretary Robert F. Kennedy Jr. fret about studies showing a broad decline in testosterone, blaming it on a crisis in masculinity and chemicals in the environment, respectively. Conservative influencers promote “T-maxxing” and direct-to-consumer testosterone injections. Republicans brag about President Donald Trump’s supposedly high testosterone levels, while slagging Democrats such as James Talarico, who’s running for the U.S. Senate from Texas, as “low T.”

Now the Pentagon is moving to enshrine these pseudoscientific ideas into military policy. Defense Secretary Pete Hegseth announced Wednesday that the department will offer testosterone deficiency screening for male soldiers 30 and older as part of their annual physicals, saying it will help ensure service members have the “right testosterone levels” to perform their “absolute best.” In a video posted with the caption “The High-T Department of War,” he said they will also have the option to receive testosterone replacement therapy.

The timing makes the announcement even more striking. The Trump administration has spent much of the past year arguing that hormone supplements are too destructive and risky to be used for gender-affirming care, particularly for transgender youth. But when the same hormone is framed as a way to make soldiers more combat-ready — and more “high T” — suddenly it becomes a government benefit.

As testosterone has moved from biology to ideology to policy, it has become increasingly divorced from science. To understand the problems with this Pentagon initiative, it’s important to understand some basic medical facts.

Testosterone levels change constantly

Testosterone is present in everyone, though at much higher levels in most men than in most women. There is no single “normal” level. The hormone is typically at its highest in the early morning, then slowly drops throughout the day. Among younger men, it can fluctuate by as much as 50%. Some studies have shown it might even be affected by the seasons. To get a good baseline, endocrinologists recommend having blood drawn at least twice on different days between 7 a.m. and 10 a.m., preferably after fasting, especially for younger men.

What this means: This is not as simple as a quick eye test. Every male soldier over 30 will need to be tested twice under very specific conditions, or the results might be skewed.

Some activities suppress testosterone

Testosterone levels can be temporarily suppressed by factors that include a bad night’s sleep, poor diet, physical exertion, severe illness, extreme stress, excessive alcohol use and certain medications. Two studies of Army Rangers found testosterone fell as much as 28% after sleep deprivation. Another found that testosterone levels dropped dramatically during the two-month Ranger School and returned to baseline after a few weeks.

What this means: Working out, eating fewer calories than you burn, going without sleep and drinking too much? Surely those are things no soldier has ever done.

There is no one ‘right’ level of testosterone

Testosterone levels vary widely. Within the normal range, that variation does not necessarily translate into meaningful differences in energy, muscle mass or facial hair. Testosterone is just one part of a much more complex hormonal system. How the body responds to it depends not only on the amount circulating in the bloodstream but also on factors such as androgen receptor sensitivity, levels of other hormones and individual genetics.