Quick Overview
Scientists measured skin-electrode contact in careful lab tests.
Sverre Grimnes and Ørjan G. Martinsen at the University of Oslo and Oslo University Hospital studied commercial electrodes, contact gels, and human skin.
They recorded impedance spectra over hours. Dry stratum corneum showed very high resistance. Fresh gel slowly lowered it as electrolytes penetrated.
Dried gel lost moisture. Contact area shrank. Current then concentrated in tiny spots, raising local current density.
These measurements explain the light burning or stinging many EMS and TENS users feel with old pads.
The work appears in the respected Elsevier book Bioimpedance and Bioelectricity Basics (2015). Norway’s strong physics tradition backs the findings.
Readers who want smoother sessions will find clear reasons to replace pads often in the full post.
We always provide direct links to the original research at the end of every article so you can review the evidence yourself.
University Research Explains The Real Reason Old TENS and EMS Pads Leave a Burning Feel
You reach for your usual pads. You place them on clean skin. The session starts. Then a light burn or tiny stings appear.
This is common with reused pads.
Trusted scientists explain the cause.
Sverre Grimnes and Ørjan G. Martinsen wrote the key book. They work at the University of Oslo and Oslo University Hospital in Norway. Their work is called Bioimpedance and Bioelectricity Basics, third edition. Elsevier published it in 2015. Norway has a long record of careful physics and biomedical research.
Their findings help us understand skin and electrodes.
Contact gel is the key.
Every pad needs a soft layer of conductive gel. This gel lets current move smoothly from the metal to the skin. Fresh gel spreads evenly. It keeps the contact area large and stable.
Old pads lose this even contact.
Sticky gel dries out over time. It loses moisture and becomes uneven. Parts of the pad pull away from the skin. The effective contact area shrinks.
Current then squeezes through the few remaining wet spots. Local current density rises sharply. Those small spots feel like light stings or a mild burn.
The top skin layer, called the stratum corneum, is naturally high in resistance when dry. Good gel slowly softens this layer. Dried gel cannot do that job well.
Strong or aged gel can also irritate.
High-salt gels penetrate skin faster. They can cause mild reddening if left too long. Dried pads collect skin oils and dirt. These raise resistance even more.
Fresh pads change the experience.
New pads bring fresh gel. Contact stays even across the whole surface. Current spreads gently. Sensation stays smooth and comfortable.
Users of TENS and EMS devices notice the difference right away. Sessions feel more pleasant. There is less need to stop and adjust.
Replacing pads and gel often keeps the contact reliable. It supports steady, even current flow every time. That is the simple, practical benefit the research points toward.
Keep your pads fresh. Your skin will thank you with quieter, more comfortable sessions.
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Research Summary
| Aspect | Information |
|---|---|
| Full title | Bioimpedance and Bioelectricity Basics |
| Edition and year | Third Edition, 2015 |
| Authors | Sverre Grimnes and Ørjan G. Martinsen |
| Author affiliations | Department of Physics, University of Oslo; Department of Clinical and Biomedical Engineering, Oslo University Hospital, Norway |
| Publisher | Academic Press (Elsevier) |
| ISBN | 978-0-12-411470-8 |
| Official link | https://www.sciencedirect.com/book/9780124114708 |
| DOI | https://doi.org/10.1016/C2012-0-06951-7 |
| Core focus | Electrical properties of tissue, electrodes, contact media, and bioimpedance measurement systems with galvanic contact |
| Measurement approach | Impedance spectra recorded on commercial pregelled electrodes and human skin over time (from onset to several hours) |
| Key finding on gel | Sticky contact gel can dry out, leading to unstable or reduced contact area and increased noise or uneven current flow |
| Key finding on skin | Dry stratum corneum dominates total impedance; wet electrolytes slowly penetrate and lower resistance over hours |
| Key finding on current | Small effective electrode area causes current constriction, raising local current density in remaining contact spots |
| Key finding on irritation | Stronger electrolyte gels penetrate faster but also produce faster skin irritation and reddening |
| Practical relevance | Explains why aged or dried pads on EMS and TENS devices often produce stinging or mild burning sensations, supporting regular replacement for even contact |
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