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Therapies · lesson 1 of 10

How to judge a therapy

Hormesis, the evidence ladder, and what 'FDA cleared' actually means.

6 min read · reviewed October 2026

Stressors, signals and claims

The products on the Therapies shelf work — or claim to work — in three different ways, and knowing which one you're buying tells you what evidence to look for:

  • Stressors: heat and cold. A short, controlled dose of discomfort that your body adapts to.
  • Signals: bright light, which tells your body clock what time it is through your eyes.
  • Direct tissue claims: red / near-infrared light and PEMF, said to act on the cells they reach.
Key concept

Hormesis: the dose makes the difference

A small dose of stress followed by recovery triggers repair and adaptation — better heat tolerance, more responsive blood vessels, a calmer reaction to cold. Too much, too often, or with no recovery tips adaptation into harm. Every therapy on this shelf has a dose, and 'more' is rarely 'better'.

The evidence ladder

1. Mechanism

Cell and animal studies show how something could work. Many product pages stop here ('activates mitochondria', 'boosts heat shock proteins'). Necessary, never sufficient.

2. Acute human response

Measures what happens during or right after a session — heart rate, a hormone spike, skin temperature. Proves your body notices; doesn't prove a lasting benefit.

3. Small randomized trials

Dozens of people, weeks long, usually measuring a marker (blood pressure, soreness, hair counts). The good ones compare against a convincing fake device. Check who funded them.

4. Large cohort studies

Thousands of people followed for years — like the Finnish sauna studies. They can link a habit to hard outcomes such as death or dementia, but can't fully separate the habit from the kind of person who has it.

5. Large trials & meta-analyses on outcomes that matter

The top rung. Few home therapies reach it. Bright light for depression is among the best supported on this shelf.

Why you can't fake a sauna — but you can fake a light panel

In plain terms

The fairest test compares a therapy against a fake version that looks and feels real. Some therapies can be faked convincingly; some can't. That changes how much you should trust the studies.

How it works →

Placebo effects are strongest for things you rate yourself — pain, mood, energy, sleep quality. Red-light panels, PEMF mats and light boxes can all be tested against sham devices that glow or hum but do nothing, so when a device maker has no sham-controlled trials, that absence tells you something. Saunas and cold plunges can't be blinded — you know you're hot or cold — so their evidence leans on long cohort studies and objective measurements.

What the studies show →

Light-therapy research shows how it's done: in a well-known depression trial, the placebo group sat in front of an inactive 'negative ion generator' that looked like a plausible treatment (Lam et al., JAMA Psychiatry, 2016). Compare that with wellness devices whose only 'studies' are customer surveys or cell experiments.

Cleared, approved, registered, 'wellness'

  • FDA approved (premarket approval): the strictest device pathway. The maker must show reasonable assurance of safety and effectiveness, usually with clinical data. Rare on this shelf.
  • FDA cleared (510(k)): the device was shown to be 'substantially equivalent' to one already on the market, for a specific stated use. New clinical trials often aren't required, and the clearance covers only that use.
  • FDA registered / listed: the company filed paperwork about its facility or product. Nobody reviewed whether it works.
  • General wellness product: low-risk items making broad claims like 'supports relaxation'. The FDA generally doesn't review these at all.
Check yourself

A red-light panel is advertised as 'FDA cleared'. What does that most reliably tell you?

  1. It's been proven to slow ageing
  2. The FDA accepted it for a specific intended use, based on similarity to an existing device
  3. It passed the FDA's strictest clinical-trial requirements
  4. Only that the company's factory is registered with the FDA
Show the answer →

B.The FDA accepted it for a specific intended use, based on similarity to an existing device

Clearance (510(k)) means 'substantially equivalent' to an existing device for a stated use — often pain relief from topical heating. It isn't approval, and it doesn't cover the other claims on the box. Look up the indication to see what was actually cleared.

Try it in the app
See hormesis in the Stress track

Why a dose of stress plus recovery makes you stronger — and why the same stressor without recovery wears you down.