The counterirritant effect: How Vicks works on a local level
Vicks VapoRub's perceived effect is often mistaken for a significant increase in blood flow. In reality, the sensation of warmth or coolness comes from its active ingredients—menthol, camphor, and eucalyptus oil—which act as counterirritants. A counterirritant works by distracting the nervous system from underlying pain signals. It does this by stimulating nerve endings in the skin, causing a mild irritation or sensation that effectively masks deeper aches and pains.
This process does involve some change in local blood vessels, but the effect is limited to the microcirculation just beneath the skin's surface and does not represent a measurable increase in overall systemic blood pressure or circulation. This is why Vicks is used for minor aches and pains or to create a feeling of decongestion rather than for serious circulatory issues.
The role of menthol and camphor
Menthol and camphor are the primary active components in VapoRub responsible for its pharmacological effects. They work through different mechanisms to create their signature sensations and local effects on blood flow.
- Menthol: This ingredient is a selective agonist for the Transient Receptor Potential Melastatin-8 (TRPM8) receptor, also known as the "cold and menthol receptor". When applied to the skin, menthol activates these cold-sensitive receptors on sensory nerves, creating the cooling sensation associated with the product. This activation, through complex pathways involving nitric oxide (NO) and other substances, leads to a local vasodilation in the cutaneous microvasculature, increasing blood flow at the application site. However, some studies also show that in areas distant from the application site, a thermoregulatory vasoconstriction (narrowing of blood vessels) can occur in response to the perceived cold.
- Camphor: Camphor is another counterirritant that interacts with Transient Receptor Potential (TRP) channels, specifically the heat-sensitive TRPV1 and TRPV3 receptors. This stimulation causes a warm sensation, and similar to menthol, it can increase local blood flow in the skin and muscle where it is applied. Camphor's action is part of the counterirritant strategy that helps alleviate minor pain.
Comparison: Vicks vs. Systemic Vasodilators
To understand why Vicks' effect on blood flow is not clinically significant for systemic circulation, consider the differences between its topical action and that of a true systemic vasodilator, such as nitroglycerin.
| Feature | Vicks VapoRub (Topical) | Systemic Vasodilator (e.g., Nitroglycerin) |
|---|---|---|
| Mechanism of Action | Activates nerve endings (TRP channels) to create local sensations and cause minor local blood vessel dilation. | Acts systemically to relax the walls of larger blood vessels, such as arteries and veins, reducing overall blood pressure. |
| Effect on Blood Flow | Minor, temporary increase in blood flow only in the skin's microcirculation at the application site. | Significant and widespread relaxation of blood vessels throughout the body, reducing the workload on the heart. |
| Therapeutic Use | Relief of minor muscle aches, joint pains, and cold-related congestion through sensory distraction. | Treatment of conditions like hypertension, heart failure, and angina (chest pain). |
| Systemic Impact | Negligible systemic absorption and no significant effect on overall blood pressure or circulation. | Directly affects systemic vascular tone and blood pressure, requiring careful medical supervision. |
| Side Effects | Skin irritation, burning sensation, potential toxicity if ingested or applied improperly. | Dizziness, headaches, hypotension, and other systemic side effects. |
Localized effects and safety considerations
The local effect of Vicks on blood flow is a byproduct of its primary function as a counterirritant, not its main therapeutic goal. For instance, in the case of muscular aches, the local vasodilation at the site of application is intended to help soothe the area and provide comfort, but this is a very minor, superficial effect. It is not equivalent to increasing blood supply to deep tissues or the cardiovascular system.
The local mechanism in practice
When you rub Vicks onto your skin, the active ingredients begin to interact with sensory nerves. The steps are as follows:
- The menthol activates TRPM8 receptors, triggering a nerve signal that is perceived by the brain as a cooling sensation. This is a neurosensory event, not a change in actual temperature.
- This sensory stimulation, along with the action of camphor, leads to a local release of vasodilatory compounds, such as nitric oxide, within the microvasculature.
- The vasodilation causes the blood vessels in the immediate area to widen, increasing local blood flow and causing a mild reddening of the skin.
- This increased superficial blood flow and the sensory distraction work together to create the feeling of relief from minor aches and discomfort.
Conclusion
Ultimately, the idea that Vicks significantly increases blood flow throughout the body is a myth. Its pharmacological effect on circulation is confined to the local microvasculature at the site of application. The sensation of relief comes from a complex interplay of sensory nerve stimulation and localized blood vessel changes, not a systemic circulatory increase. For this reason, Vicks is considered a topical analgesic and cough suppressant with no meaningful impact on overall cardiovascular health. It's important to use it as directed and never ingest it or apply it to mucous membranes, which can lead to toxic systemic absorption of camphor.
For more in-depth scientific information on the vascular effects of menthol, refer to the detailed review published in Frontiers in Physiology.
