Which specific skin receptors are stimulated when applying counterirritants?

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

How is the analgesic effect of counterirritants explained at the CNS level?

The central analgesic effect is explained by the convergence of two excitation streams. In the spinal cord segments and higher CNS centers, the impulse stream from the affected organ meets the stream from cutaneous receptors induced by the irritant. This interaction suppresses pain perception. Additionally, counterirritant analgesia is thought to involve the activation of central antinociceptive mechanisms via supplementary afferent input.

Is involvement of the brain or spinal cord required for the axon reflex?

No, antidromic impulse propagation along axon branches occurs locally without the participation of CNS structures.

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

Allyl isothiocyanate (essential mustard oil) stimulates cutaneous exteroceptors.

Which peptides are released during sensory nerve stimulation?

Antidromic impulse conduction leads to the release of substance P and calcitonin gene-related peptide (CGRP).

Home › Pharmacology › Counterirritant Effect

Counterirritant Effect

For medical students2 min readUpdated 2026-10-10

Counterirritant effect is a pharmacological phenomenon characteristic of irritant agents that act on afferent nerve endings. The process is based on the local stimulation of cutaneous receptors, which triggers a cascade of neuroreflex and vascular responses that improve tissue trophic function.

Drug ClassAgents affecting afferent innervation

Basic MechanismLocal stimulation of the axon reflex

Primary IndicationsMusculoskeletal and nervous system disorders

Key EffectLocal hyperthermia and arterial hyperemia

Classification and Major Representatives

Drugs with counterirritant potential belong to agents affecting afferent innervation (irritant agents). Various pharmaceutical formulations and combinations are used in clinical practice:

Mustard plasters (Sinapisma).
Nonivamide/nicivamide ointment (e.g., Finalgon).
Turpentine ointment (Oleum Terebinthinae).
Combination products containing menthol.
Solutions and liniments (e.g., Menovazin, Valadol).

Physiological Mechanisms: The 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 sequence of action, using mustard plasters as an example, proceeds as follows:

Receptor Stimulation. Essential mustard oil (allyl isothiocyanate) stimulates cutaneous exteroceptors at the application site.
Antidromic Conduction. A nerve impulse is generated and propagates antidromically along axon branches. Notably, this process occurs exclusively at the local level without involving central nervous system (CNS) structures.
Mediator Release. Specific neuropeptides—substance P and calcitonin gene-related peptide (CGRP)—are released from the terminals of sensory nerve fibers.

Effects on Hemodynamics and Thermoregulation

A direct consequence of the axon reflex is the alteration of local blood flow and heat dissipation. The release of neuropeptides provokes sustained vessel dilation (vasodilation).

Arterial hyperemia develops at the application site. Due to increased blood flow, skin temperature rises under the mustard plaster or ointment layer. This local hyperthermia plays a crucial role: it significantly improves the trophic supply of underlying tissues and provides the counterirritant effect, reducing pathological symptoms.

Additional Properties and Indications

Beyond the primary neuroreflex influence, certain agents demonstrate auxiliary pharmacological effects:

Antiseptic action (characteristic of turpentine ointment).
Antibacterial action (mustard components exhibit marked phytoncide activity; this effect contributes significantly to pharmacodynamics, particularly upon inhalation of essential oil vapors during the procedure).

Indications for Use: Irritants with a counterirritant effect are actively used for peripheral nervous system and musculoskeletal disorders. Major conditions include:

Radiculopathy.
Various forms of myositis.
Arthritis.

Frequently asked questions

Which specific skin receptors are stimulated when applying counterirritants?: Cutaneous exteroceptors are stimulated upon application. Excitation of these receptors (e.g., by essential mustard oil) triggers the basic mechanism of the axon reflex. This leads to antidromic impulse conduction along axon branches and the local release of neuropeptides (substance P, calcitonin gene-related peptide) from sensory nerve terminals.
How is the analgesic effect of counterirritants explained at the CNS level?: The central analgesic effect is explained by the convergence of two excitation streams. In the spinal cord segments and higher CNS centers, the impulse stream from the affected organ meets the stream from cutaneous receptors induced by the irritant. This interaction suppresses pain perception. Additionally, counterirritant analgesia is thought to involve the activation of central antinociceptive mechanisms via supplementary afferent input.
Is involvement of the brain or spinal cord required for the axon reflex?: No, antidromic impulse propagation along axon branches occurs locally without the participation of CNS structures.
Which chemical substance is responsible for the effect of mustard plasters?: Allyl isothiocyanate (essential mustard oil) stimulates cutaneous exteroceptors.
Which peptides are released during sensory nerve stimulation?: Antidromic impulse conduction leads to the release of substance P and calcitonin gene-related peptide (CGRP).

Go deeper

Mechanisms of substance P release and its physiological role
Specific actions of calcitonin gene-related peptide (CGRP)
Phytoncide activity of allyl isothiocyanate
Differences between antidromic and orthodromic impulse conduction
Comparative pharmacology of turpentine ointment and nonivamide/nicivamide ointment