What the research actually says about heat.
This page sets out the described mechanism, the trial evidence behind it, and the two findings in that same evidence that cut against us. None of it is a claim about our product. It is a claim about heat, which has been the first piece of advice for cramps for about as long as there has been advice.
It is not just that warmth is nice.
Reaching for a hot water bottle is the oldest advice there is for cramps, and it turns out there is a reasonably well described reason it works. Heat does something specific to the way a pain signal travels.
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Heat switches on a receptor. Skin carries heat receptors called TRPV1. Physiologists at University College London found that warmth above roughly 40 °C on the skin near where pain is felt is enough to activate them.
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That receptor blocks a pain receptor. Once active, TRPV1 blocks P2X3, which is the receptor that carries the pain signal when ATP leaks out of damaged cells. The signal gets interrupted rather than masked.
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It works about a centimetre deep. Surface heat in the 40 to 45 °C range reaches roughly one centimetre into the tissue underneath. That is the layer this is working on, which is also why it has to be held against the skin rather than waved nearby.
- Against no treatment
- 4.0points lower on a 10 point pain scale, pooled across the trials.
- Against painkillers alone
- 0.72standardised effect size in favour of the heat patch.
- Trials behind that
- 6randomised controlled trials, reviewed in 2018.
Two things the same review found that we are not going to leave out. The authors called their own evidence suggestive, because it rests on relatively few trials with small numbers of people in them. And when a heat patch was used on top of ibuprofen, it did not beat an unheated patch on top of ibuprofen. Where ibuprofen already works, heat may not be adding much.
Heat is also what the NHS lists first for period pain, before it gets to painkillers: a heat pad or a hot water bottle on the stomach, a warm bath, gentle movement. Mayo Clinic says much the same. None of that is a claim about this particular product. It is a claim about heat, and our product is a way of carrying heat around that does not need a kettle or a socket.
One honest note on the numbers. The research above describes temperature measured at the skin. The 50, 55 and 60 °C quoted on the product page describe the heating element, which is not the same measurement once it has travelled through a fabric pad. Start on the lowest setting.
Sources: UCL, Heat halts pain inside the body, 2006 · Jo and Lee, Heat therapy for primary dysmenorrhea, Scientific Reports, 2018 · NHS, Period pain · Mayo Clinic, Menstrual cramps
Nothing on this page is a statement about what any particular person should do. Heat is not a diagnosis and it does not replace one.