Red Light Therapy vs. a TENS Unit: Which Is Better for Pain?

Short answer: a TENS unit blocks the feeling of pain while it's running, and red light therapy works on the tissue underneath so the area feels better between sessions. If you want fast, temporary distraction from a flare-up, TENS. If you want to work on the sore joint or muscle itself over a few weeks, red light. Plenty of people end up using both.

If you've been shopping for at-home pain relief, you've probably seen both sitting in the same FSA-eligible aisle at similar prices. They look like they do the same job. They don't. Here's the difference in plain English, and how to figure out which one belongs in your drawer.

What does a TENS unit actually do?

A TENS unit sends a mild electrical current through sticky pads on your skin. TENS stands for transcutaneous electrical nerve stimulation — "through the skin, electrical, nerve." That current stimulates the nerves in the area, which is thought to interfere with the pain signals traveling to your brain and possibly nudge your body to release its own endorphins.

The experience is unmistakable: a buzzing, tingling, sometimes tapping sensation. Turn it up and your muscle may twitch. Turn it off and the sensation stops immediately — and for many people, so does the relief. That's the core thing to understand about TENS. It is a symptom manager, not a tissue treatment. It's genuinely useful for that, and it's fast.

What does the research say? An overview of Cochrane Reviews on TENS for chronic pain concluded that the evidence base was too low-quality to say confidently whether TENS beats a sham device, and found no reliable evidence that different frequencies or electrode placements matter much (Gibson et al., Cochrane Database of Systematic Reviews, 2019). That doesn't mean TENS doesn't help anyone — millions of people swear by it, and physical therapists still hand them out. It means the science hasn't nailed down how much of it is the current and how much is everything else.

What does red light therapy actually do?

Red light therapy — the clinical name is photobiomodulation — puts specific wavelengths of red and near-infrared light onto your skin. No heat that burns, no current you feel. Red light around 660nm is absorbed in the skin and shallower tissue. Near-infrared around 850nm travels deeper, into muscle and joint tissue.

The working theory is that this light is absorbed by your cells' mitochondria and gives their energy production a small nudge, which in turn supports local circulation and helps calm inflammation in the area. You don't feel it happening. That's the honest tradeoff: TENS gives you an obvious sensation and immediate distraction, red light gives you nothing to feel and asks you to be patient for a few weeks.

On the evidence side, a systematic review with meta-analysis in Physical Therapy found photobiomodulation reduced pain and disability in people with knee osteoarthritis compared with sham treatment (Physical Therapy, 2024). Another meta-analysis found that low-level laser therapy combined with exercise therapy improved pain and function in knee osteoarthritis more than exercise alone (PubMed, 2023). Worth noting: results in these trials depend heavily on dose and consistency, and red light is studied as an adjunct alongside movement and good care — not a replacement for either.

Which one works faster?

TENS, clearly. You feel something within seconds of turning it on. If your lower back seizes up on a Tuesday afternoon and you need to get through a workday, that's real value.

Red light works on a different clock. Most people using it for joint or muscle discomfort do 10–20 minute sessions, three to five times a week, and start forming an opinion somewhere in week two or three. If you try it twice and quit, you haven't really tried it. This is the single most common mistake we see.

Which one is better for arthritis, an old knee, or a nagging joint?

For a chronically cranky joint you want to improve rather than just mute, red light is the better fit. The knee osteoarthritis research above is the strongest evidence base red light has, and joints are exactly where near-infrared's deeper reach matters.

For a knee, the Red Light Therapy Belt straps directly around the joint so you're not holding anything in place. If the trouble is spread across your back, hips and shoulders — or you'd rather treat several areas at once — a panel makes more sense. The FX500 ($269.99) is our full-body flagship; the smaller FX300 ($199.99) is built for targeting one area at a time.

Which one is better for feet and neuropathy?

Red light is usually the easier choice for feet, mostly for practical reasons. Sticky TENS pads and the bottoms of your feet are a frustrating combination — they slip, they don't conform, and placement around the toes is guesswork. The Red Light Therapy Slippers ($199.99) surround the whole foot, toes and heel included, and you can wear them on the couch.

If your foot discomfort is nerve-related, talk to your doctor first regardless of which device you pick. Reduced sensation changes the safety calculus for anything applied to the feet.

Can you use TENS and red light therapy together?

Yes, and it's a reasonable combination — just don't run them on the same spot at the same time. They're not competing for the same job. A common pattern: red light most days as maintenance, TENS pulled out on bad days when you need something to take the edge off right now.

Keep the electrodes and the light session separate. Wet gel pads and an LED device pressed together is needless complication with no upside. Do one, then the other.

Are both FSA and HSA eligible?

TENS units and red light therapy devices are both commonly FSA/HSA eligible, though some plans want a letter of medical necessity for the red light side. Our full walkthrough is here: Is red light therapy FSA eligible? How to pay with your FSA or HSA card. Everything in our FSA/HSA eligible collection is set up to run through a benefits card at checkout.

Frequently asked questions

Does red light therapy hurt like TENS can?

No. Red light therapy produces no electrical sensation at all. Some devices feel mildly warm. TENS, by contrast, is meant to be felt — and turned up too high, it can sting or cause an uncomfortable muscle twitch.

Is one safer than the other?

Both are generally well tolerated by healthy adults. TENS has firmer restrictions: people with pacemakers or other implanted electrical devices are typically told to avoid it, as are pregnant women in most cases. Red light has fewer hard contraindications but its own cautions, including photosensitizing medications and eye protection when using a bright panel. Check with your provider either way.

How long until red light therapy helps with pain?

Give it three to four weeks of consistent use — roughly 10–20 minutes per session, three to five sessions a week. Some people notice looser, less achy joints sooner. If you're only using it when you remember to, you won't get a fair read.

Which is cheaper?

Basic TENS units are usually less expensive up front, but they need replacement electrode pads on an ongoing basis. Red light devices cost more at purchase and have no consumables. If you want to spread the difference over time, count the pads.

Can I use red light therapy through clothing?

Light needs to reach skin to do anything. A thin layer of fabric blocks a meaningful amount of it, so place devices against bare skin where you can. A wrap like the Red Light Therapy Belt is designed to sit directly on the area.

What if I'm not sure which device fits my situation?

Take two minutes with our device finder quiz. It asks where it hurts and how you'd like to use it, then points you to the right product. You can also browse the full red light therapy collection or the wearables collection if you already know you want something that straps on.

So which should you buy?

Buy a TENS unit if what you need is an off-switch for acute pain and you're fine with the relief ending when the device does. Buy red light therapy if you're trying to change how a joint or muscle feels day to day, and you can commit to a few weeks of short, boring sessions.

For most of the people we hear from — the ones with an old knee, a stiff shoulder, or a back that's been complaining for years — red light is the better long game. TENS is a good thing to have in the drawer for the bad days.

Lights on, pain off.

This article is for general education and is not medical advice. Red light therapy devices are intended for general wellness and are not intended to diagnose, treat, cure, or prevent any disease. Always check with a qualified healthcare provider before starting a new therapy.