The story of living forever — or, as we explained in Part 1 of our Longevity series, living healthier for longer — has become one of the biggest conversations of the decade. And it is hardly surprising: over the past few years, health and wellness have shifted from niche interests to full-blown obsessions. People don't just read about longevity anymore; they build routines around it, book clinic appointments and, perhaps most importantly, happily pay for it. The result? The longevity economy is now worth trillions of dollars, being roughly 15 times the size of the global video games industry.

In Part 1, we put four of longevity's most talked-about treatments under the microscope. Now we are back with some of the biggest names we missed: therapeutic plasma exchange (TPE), red light therapy and hyperbaric oxygen therapy (HBOT).

With help from medical professionals, we are figuring out what is actually backed by science — and what is mostly backed by a very good marketing team.

In Part 1 of our Longevity series, we started with the theory (if you missed it, it is probably worth starting there first). This time, before diving into the treatments themselves, I want to answer a slightly different question: why are so many people willing to invest in longevity in the first place? After all, while the longevity industry is projected to be worth $27 trillion by 2030, many of the therapies making headlines are still being studied, and very few come with anything close to a 100% guarantee. So where does all the hype come from?

Part of the answer is simple demographics. For the first time in history, there are more people aged over 65 than children under five worldwide. By 2050, around one in six people will be over the age of 65, compared with roughly one in ten today. As that population grows, so does the number of people looking for ways to stay healthier for longer. And when there is no guaranteed solution, even the possibility of slowing ageing can be enough. Longevity isn't selling certainty — it is selling hope.

Then there is money. Longevity has become one of Silicon Valley's favourite bets. Billionaires are funding research into cellular reprogramming, senescent cells and age-related diseases, turning what was once a niche scientific field into a serious investment category. And where investment goes, attention — and excellent marketing — usually follow.

Finally, longevity is no longer just for people in their sixties and seventies. Prevention has become aspirational. Millennials and Gen Z have grown up believing that the best treatment is the one you never need. We don't wait for cavities before brushing our teeth or for heart disease before exercising, so applying the same logic to ageing suddenly doesn't seem so far-fetched.

Wearables have only accelerated that shift. Smartwatches, rings and health apps have turned sleep, recovery, heart rate and stress into numbers we check every morning. Once something becomes measurable, it also becomes optimisable.

All of this brings us to today's question: with so many treatments promising to slow ageing, improve healthspan or even rewind your biological clock, which ones actually deserve your attention — and which are racing ahead of the science?

Unlike most longevity therapies, TPE wasn't developed with healthy ageing in mind. It was already an established hospital procedure used to treat serious autoimmune and blood disorders, including myasthenia gravis, Guillain–Barré syndrome and a handful of equally intimidating diagnoses.

The treatment works by taking blood from the patient and passing it through a machine that separates the blood cells from the plasma — the yellowish liquid carrying proteins, hormones, antibodies and thousands of signalling molecules. The plasma is then removed, replaced (usually with albumin), and the blood is returned to the body.

None of that sounds remotely connected to longevity. So how did a treatment designed for seriously ill patients end up becoming one of the most talked-about anti-ageing therapies?

It all started with mice. Scientists had long noticed that ageing comes with a build-up of inflammatory molecules in the bloodstream. So they began wondering: perhaps ageing isn't just about losing the "good" molecules over time. Perhaps it is also about accumulating too many of the bad ones.

To test the idea, researchers turned to one of biology's strangest experiments: parabiosis. A young and an old mouse were temporarily connected so that they shared the same circulatory system. The older mice appeared healthier, their tissues repaired more efficiently, and headlines quickly declared that young blood might hold the secret to rejuvenation.

But the story didn't end there. As more studies followed, another explanation began to emerge: maybe the older mice weren't benefiting because young blood contained some magical rejuvenating factor. Maybe they were improving simply because some of the age-related molecules had been removed altogether from their own circulation. And that is exactly how TPE found itself on longevity's radar.

The catch? The evidence in humans is far less convincing. One of the most discussed studies followed 42 participants, with an average age of around 65, and reported improvements in several biological markers associated with ageing after plasma exchange. Promising? Certainly. Convincing enough to recommend the treatment to healthy people? Not yet. The study was small, lasted only a short time, and wasn't designed to show whether participants actually lived healthier — or longer.

So, does TPE actually work? Absolutely — for the autoimmune and blood disorders it was designed to treat. When it comes to slowing ageing in otherwise healthy people, however, the answer is still much less certain.

And one final thing to remember if you are considering TPE: unlike a supplement or a red light mask, this is an invasive hospital procedure that carries real risks.

Most of us know red light therapy from the glowing LED face masks that have taken over social media. But those masks are only one small part of the story. The same technology is also used to help treat hereditary hair loss by exposing the scalp to specific wavelengths of light, support muscle recovery after exercise, ease certain types of joint pain and, in some cases, promote wound healing. In medical and scientific literature, however, it is more commonly referred to as photobiomodulation. So what exactly is it doing?

Unlike UV light, red and near-infrared light don't tan the skin or damage DNA. Instead, they penetrate the tissues and appear to help cells produce energy more efficiently while reducing inflammation and supporting the body's natural repair processes.

So what does that have to do with longevity?

The idea is fairly simple: many of these processes become less efficient as we age. Our cells produce less energy, inflammation gradually increases and the body becomes slower at repairing itself. Because red light therapy appears to support these functions, it has become one of the most talked-about treatments in the longevity world.

So, does it actually work? The short answer is yes — but only for certain things.

Red light therapy has the strongest evidence for improving skin health and helping treat hereditary hair loss. Studies have also reported benefits for wound healing, some types of pain and, potentially, muscle recovery, although the results are generally modest rather than dramatic.

When it comes to longevity itself, however, the picture changes. Researchers are exploring whether red light therapy could influence age-related processes such as inflammation, cognitive function and cellular repair, but the evidence is still in its early stages. In other words, red light therapy is a promising treatment for several specific medical and cosmetic uses — but, for now, not a proven longevity therapy.

Hyperbaric oxygen therapy is one of the more unusual treatments you will come across. You climb into a sealed chamber, the pressure gradually rises to around two or three times normal atmospheric pressure, and you breathe pure oxygen for about an hour.

HBOT has been used in hospitals for decades to treat serious conditions including carbon monoxide poisoning, gas embolism and radiation tissue injury. Under these conditions, far more oxygen dissolves into the blood, allowing it to reach tissues that would otherwise struggle to get enough. So how did a treatment for serious medical conditions become one of longevity's biggest talking points?

While studying HBOT for its medical uses, researchers noticed something intriguing: the treatment appeared to reduce inflammation, improve blood vessel function and activate some of the body's repair mechanisms — at least in animal studies. Naturally, the next question was: could those same effects help people stay healthier as they age?

That question catapulted HBOT into the longevity spotlight in 2020, when an Israeli study put 35 healthy adults over the age of 64 through 60 sessions over 90 days. Researchers reported longer telomeres — protective caps at the ends of chromosomes linked to ageing — and fewer senescent, or "zombie", cells. The findings made headlines around the world, with some hailing HBOT as a breakthrough that could help people live longer or even reverse ageing.

The excitement didn't last long though. The study was small, lacked a randomised control group and measured biological markers rather than actual health or lifespan. Since then, the bigger picture has been far more cautious. While some studies have reported encouraging biological effects, none has convincingly shown that HBOT slows ageing or helps healthy people live longer. For now, larger clinical trials are still needed.

Today, HBOT remains one of the biggest names in the longevity world, with many clinics continuing to offer it despite the evidence still falling short of proving it slows ageing or helps healthy people live longer. But despite its good safety profile when performed in accredited medical centres, major medical organisations don't currently recommend HBOT as an anti-ageing treatment for healthy people.