A counterirritant is an agent applied to the skin or mucous membranes that produces superficial irritation intended to relieve pain or discomfort in underlying tissues, typically muscles, joints, or tendons.
Mechanism of Action
| Fiber Type | Signal Type | Diameter | Speed | Myelination | Example Sensation |
|---|---|---|---|---|---|
| A-beta | Touch, pressure, vibration | Large | Fastest (35–90 m/s) | Myelinated | Rubbing skin, menthol cooling |
| A-delta | Sharp pain, cold | Medium | Medium (5–30 m/s) | Myelinated | Sharp initial pain, icy pain |
| C fibers | Dull pain, heat, itch | Small | Slowest (0.5–2 m/s) | Unmyelinated | Burning pain, soreness |
When you apply menthol or camphor, they stimulate A-beta fibers and sometimes A-delta fibers—which send signals much faster than the slower, pain-transmitting C fibers.
So:
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Menthol says: “Cool! Cool! Cool!”
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C fibers try to say: “Pain! Ache! Throb!”
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The brain receives the cooling message first and gets distracted.
Because of this prioritized signal processing, your brain’s perception gets dominated by the fast “cool” or “warm” signals, masking the dull pain.
And the other mechanism that plays it’s role in this is explained by Gate Control Theory of Pain