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June 20, 2025—Risky testosterone therapy, whales are blowing bubbles, and SpaceX's Starship explodes on its stand. —Andrea Gawrylewski, Chief Newsletter Editor | | A humpback whale known as Kараул (Watchtower) produced this bubble ring in Hawaii in 2020. Molly Gaughan | | Testosterone replacement therapy—prescription supplements in the form of pills, patches, injections or implantable pellets—is booming: The global market has been estimated at $1.9 billion. Podcasters, social media influencers and ads praise the therapies' benefits, but rarely mention its risks. Why this matters: When men with testosterone levels higher than the proposed "low" ranges are prescribed TRT, they may experience an increased risk of its harmful side effects with little to no benefits. This includes but isn't limited to an increased risk of infertility, shrunken testicles, bone fractures and an abnormal blood condition known as erythrocytosis. | | Violet Frances; Source: Abraham Morgentaler (scientist reviewer) | | A dosing problem: For men with seriously low levels of the hormone, the therapy can improve mood, energy levels, sex drive, and more. But many medical communities disagree on what constitutes "low." The American Urological Association suggests that anything below 300 ng/dL is "low," but other groups have "normal" ranges that overlap. For example, both the Endocrine Society and the European Academy of Andrology suggest that levels under 300 ng/dL, down to 231 ng/dL, are normal. This uncertainty grants clinics the leeway to prescribe the therapy for men above the proposed "low" ranges. What the experts say: Testosterone's cultural connection to stereotypical ideas of masculinity (bigger muscles, higher sex drive) makes it emotionally appealing to many men. However, according to Justin Dubin, a urologist at Memorial Healthcare System in southern Florida, the majority of the testosterone information on TikTok and Instagram is horrible, horrendous and inaccurate. —Andrea Tamayo, newsletter intern More: Journalist Stephanie Pappas wrote about the testosterone boom for our July/August issue. Listen to her interview today on our podcast Science Quickly. | 12 min listen | | | | |
A Special Event for Scientific American Subscribers | | The fast fashion industry is under fire for its environmental toll and exploitative labor practices. But a wave of change is rising. Join journalist Jessica Hullinger in conversation with Scientific American editor Jennifer Schwartz as they spotlight the innovators and movements reshaping fashion—from botanical dyes and local supply chains to upcycling and repair services. You'll also get a comprehensive guide to making truly sustainable fashion choices. | | | | |
- If you read Today in Science this week, you should do great on the science quiz. Also check out today's Spellements, and remember, if you spot any words missing from the puzzle, email them to games@sciam.com. This week, Robert W. from Western Australia sent in mallee, which is a bushy Australian eucalyptus plant. Love it!
| | MOST POPULAR STORIES OF THE WEEK | | - Mathematicians Come Up with 'Mind-Blowing' Method for Defining Prime Numbers | 5 min read
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- Quantum Computers Simulate Particle 'String Breaking' in a Physics Breakthrough | 3 min read
| | Every Friday in summer we'll recommend a great, freshly-published science read. Tell us what you're reading or if you try any of the books we suggest! | | Everything is Tuberculosis: The History and Persistence of Our Deadliest Infection By John Green. Crash Course Books, March 2025.
 Tuberculosis is thousands of years old and has been cured since the 1950s, yet globally about 10 million people contract it every year (some 1.25 million die). It's a bacterial infection—we have good antibiotics to fight it, thanks, in part, to a forgotten group of black nurses in Staten Island who cared for TB patients during the early 20th century and participated in drug trials, meticulously recording patient data, which was essential for the development of the cure. In his latest book, Everything is Tuberculosis, author John Green argues that TB is very much still a modern-day crisis. He follows the case of a nine-year-old TB patient in Sierra Leone, whose years-long struggle became an emblem of how diseases like TB thrive in poverty and inequitable societies. "We do not live up to our promise that all people have been created equal. And that's why we still have tuberculosis," he said in an interview on our podcast Science Quickly. —Brianne Kane
| | Today is the summer solstice, the longest day of the year in the Northern Hemisphere and the official start of summer. Interestingly, meteorologists consider June 1 the beginning of summer, mostly to have nice even months over which to track weather trends, as my colleague Andrea Thompson explains. Whenever summer kicks in for you, we're getting more of it every year because of the warming climate. In the coming months, as the hot temps settle in, Scientific American will have plenty of coverage of how our planet is changing and how to stay cool. | | Thank you for joining me on a journey of science discovery this week. Send any thoughts to: newsletters@sciam.com. Have a great weekend. —Andrea Gawrylewski, Chief Newsletter Editor | | | | |
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