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Pharmacology · Special Pharmacology

Counter-irritant Action

Counter-irritant action is a pharmacological effect characteristic of irritants that act on afferent nerve endings. The process is based on the local stimulation of skin receptors, which triggers a chain of neuroreflex and vascular reactions that improve tissue trophism.

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Drug groupAgents affecting afferent innervation
Basic mechanismStimulation of the axon reflex at the local level
Site of actionDiseases of the musculoskeletal system and nervous system
Key effectLocal hyperthermia and arterial hyperemia
3 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Classification and main drugs

Drugs with a counter-irritant potential belong to the category of agents affecting afferent innervation (the group of irritants). Various dosage forms and combinations are used in clinical practice:

  • Mustard plasters (Sinapisma).
  • Finalgon ointment.
  • Turpentine ointment.
  • Combination drugs containing menthol.
  • Solutions and drops (e.g., Menovazin, Validol).

Physiological mechanisms: axon reflex

The efficacy of these drugs is based on a complex neuroreflex reaction. The fundamental mechanism is the stimulation of the so-called axon reflex. The logic of the drug's action, taking mustard plasters as an example, unfolds as follows:

  1. Receptor irritation. Mustard essential oil (allyl isothiocyanate) acts on skin exteroceptors at the application site.
  2. Antidromic conduction. A nerve impulse arises and propagates antidromically, i.e., along the branches of the axon. It is important to note that this process occurs exclusively at the local level, without involving central nervous system (CNS) structures.
  3. Release of mediators. Specific neuropeptides—substance P and calcitonin gene-related peptide—are released from the endings of sensory nerve fibers.
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Impact on hemodynamics and thermoregulation

A natural consequence of the axon reflex is a change in local blood circulation and heat transfer. The release of neuropeptides triggers persistent blood vessel dilation (vasodilation).

Arterial hyperemia develops at the application site. Due to increased blood inflow, skin temperature rises under the mustard plaster or ointment layer. Such local hyperthermia plays a crucial role: it significantly improves the trophism of underlying tissues and provides the very counter-irritant effect, reducing the severity of pathological symptoms.

Additional properties and indications

In addition to the primary neuroreflex effect, certain agents exhibit concomitant pharmacological effects:

  • Antiseptic action (characteristic of turpentine ointment).
  • Antibacterial action (mustard components possess pronounced phytoncide activity; this effect contributes significantly to pharmacodynamics, especially during inhalation of essential oil vapors during the procedure).

Indications for use: Irritants with a counter-irritant effect are actively used for diseases of the peripheral nervous system and musculoskeletal system. The main nosologies include:

  • Radiculitis.
  • Various forms of myositis.
  • Arthritis.

Briefly: answers to topical questions

What specific skin receptors are stimulated when irritants are applied?

When irritants are applied, skin exteroceptors are stimulated. Excitation of these receptors (e.g., by mustard essential oil) triggers the basic mechanism of the axon reflex. This leads to antidromic impulse conduction along axon branches and the release of neuropeptides (substance P, calcitonin gene-related peptide) from sensory nerve endings at the local level.

How is the analgesic effect of counter-irritants explained at the CNS level?

The analgesic effect at the CNS level is explained by the interaction of two excitation streams. In the spinal cord segments and higher CNS centers, the impulse stream from the affected organ meets the stream from skin receptors induced by the irritant. As a result of this interaction, pain perception is suppressed. It is also assumed that counter-irritant analgesia is provided through the activation of central nervous system antinociceptive mechanisms due to additional afferent input.

Class and exam questions

Is the participation of the brain or spinal cord required for an axon reflex to develop?

No, the occurrence of antidromic impulse conduction along axon branches takes place at the local level without the participation of CNS structures.

Which chemical substance is responsible for the effect of mustard plasters?

Exteroceptor irritation in the skin is caused by allyl isothiocyanate, a mustard essential oil.

Which peptides are released upon stimulation of sensory nerves?

During antidromic impulse conduction, substance P and calcitonin gene-related peptide are released.

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What else to study on this topic

  • Mechanisms of substance P release and its physiological role
  • Specifics of calcitonin gene-related peptide (CGRP) action
  • Phytoncide activity of allyl isothiocyanate
  • Differences between antidromic and orthodromic impulse conduction
  • Comparative characteristics of turpentine ointment and Finalgon ointment

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