Medical clinics are popping up across the country promising to help clients live longer and better—so long as they can pay. Longevity clinics aim to do everything from preventing chronic disease to healing tennis elbow, all with the goal of optimizing patients’ health for more years. Clients pay as much as $100,000 a year for sometimes-unproven treatments, including biological-age testing, early cancer screenings, stem-cell therapies, and hair rejuvenation.

The centers capitalize on Americans’ obsession with living longer. Many doctors caution that some clinics’ treatments lack robust scientific evidence or introduce health risks. One researcher said, “Anybody who is treating your toenails can say they’re contributing to longevity.”

People who visit these clinics are often wealthy people in their 40s to 60s who are seeing signs of aging. Several providers say they have noticed clientele trending as young as 20-somethings in recent years.