— Ariela Basson/Fatherly; Stocksy

Virility, strength, dominance, perhaps aggression — these are the traits popular culture associates with high testosterone. But what does it actually mean for men’s health and behavior to have high levels of the sex hormone? And how common is high testosterone, actually?

The first thing to understand about testosterone levels is that there is a wide range for what is considered “normal.” Anywhere from 300 to 1,000 nanograms per deciliter of blood (ng/dL) is considered A-okay, according to Mount Sinai. But even this range is controversial — some men fall outside of it and stay perfectly healthy.

Among men with testosterone levels at the high end of this range, or even above it, “there’s a big difference between people who have it endogenously, meaning they’re making it on their own, and people who get it exogenously, meaning they’re taking a drug or supplement,” says Amin Herati, M.D., a urologist and the director of male infertility and men’s health at Johns Hopkins Medicine.

Most of what we know about high testosterone is based on athletes using testosterone for performance enhancement or men taking testosterone replacement therapy for low T, according to Harvard Medical School. For the former, high levels of the hormone do seem to have an impact on behavior and personality. “At the extremes, people experience irritability, depression, and anxiety,” Herati says. Other problems include low sperm counts, shrinking of the testicles, abnormally high blood-cell counts, heart damage, increased risk of heart attack, and more.

Some men taking testosterone replacement therapy experience similar effects. In a 2004 study of 28 men receiving testosterone therapy, both the men and their partners reported a small increase in anger and hostility two weeks after a single injection.

Among people who aren’t taking supplements or therapies to enhance testosterone, abnormally high levels are “rare,” Herati says. Only 2.5% of men naturally have levels higher than 916 ng/dL, according to a study of more than 6,000 European and American men between the ages of 19 and 39. Occasionally, extremely high testosterone levels can be a symptom of certain cancers and adrenal disease, or a medication side-effect. “We’ll do investigations of their adrenal gland if levels are really, really high [above 1,200 ng/dL],” Herati says.

But for most men with naturally high testosterone, it’s not a problem. It might even be a blessing — after all, one third of men older than 45 eventually develop low testosterone, which is associated with a wide range of mood and health effects. “In general, [men with high testosterone] are just blessed with good cells that produce testosterone really well,” Herati says.

If you are one one of these genetically blessed individuals, are you actually more likely to be uber-macho or aggressive, as popular understandings would suggest?

There is some truth to the idea that high testosterone impacts mood and behavior. It can both increase and decrease levels of dopamine and serotonin — brain chemicals that keep us motivated and help us feel good. In a study of 54 men and women published in the Indian Journal of Psychological Medicine, men with higher testosterone levels had higher scores in “criminal thinking” and “compulsiveness.” In another study of 41 men in Senegal, men who scored in the top 25% for extraversion, according to a personality test, had testosterone levels 29% higher than the rest of the population. But Herati notes that these study sizes are small and don’t account for the myriad of other factors that affect mood and behavior.

It would be impossible, based on this research, to take any individual man and attribute his mood and personality traits to his testosterone levels. In other words, Herati says, the overall evidence for a link between high testosterone and those Hulk-like personality traits — is mostly a myth.