355 Sensitive skin panels
LAST with functional magnetic resonance imaging (fMRI) may allow a more objective
assessment 19 however, this approach is not feasible for routine use. In any case, a discrepancy
exists between the lactic acid response and the self-perception of sensitive skin.20 Therefore,
it is recommended to combine LAST with a concurrent questionnaire.16
CAPSAICIN TEST
The capsaicin test was more recently introduced to assess the hyperactivation of Transient
Receptor Potential Vanilloid 1 (TRPV1) in individuals with sensitive skin.21 TRPV1 is
a cationic ion channel activated by heat and capsaicin. In this test, a 0.075% capsaicin
emulsion is applied, and similar to the LAST, it relies on a subjective individual pain scale
for evaluation.
Interestingly, the Capsaicin Detection Threshold (CDT) test combines the specific reactivity
of sensitive skin to capsaicin, the simplicity of the LAST application, and a threshold
detection method. Unlike traditional methods, it no longer quantifies the intensity of the
response but instead determines detection thresholds for topically applied capsaicin. The
test uses five capsaicin concentrations in a 10% ethanol aqueous solution: (3.16 × 10−5%,
1 × 10−4%, 3.16 × 10−4%, 1 × 10−3%, 3.16 × 10−3%).21 The method used to attain the
detection threshold consists of applying increasing concentrations of capsaicin onto the
nasolabial folds (with a 3-minute interval between each application). The vehicle is
simultaneously applied following a split-face, single-blind plan. The test is stopped as soon
as the subject reports a specific sensation on the capsaicin side.
NEUROPHYSIOLOGICAL TECHNIQUES
These methods are used for studying the impairment of somatosensory function in
neurologic diseases. They are based on different stimuli: thermal (cold, warm), electrical,
or mechanical. Their use is more restricted to specialized centers, and they are rarely used
to assess sensitive skin.
CURRENT PERCEPTION THRESHOLD (CPT)
Sensitivity evaluations using the Current Perception Threshold (CPT) method distinguish
between types of nerve fibers based on their activation by three different current frequencies,
facilitated by the Neurometer® CPT® device (Neurotron Inc., Aurora, CO, USA).
Transcutaneous electrical stimuli are delivered through two electrodes. The frequencies
produced by the Neurometer® CPT® selectively stimulate three subsets of nerve fibers:
• 2000 Hz: Activates large myelinated Aβ fibers, responsible for touch and pressure
sensation.
• 250 Hz: Activates small myelinated Aδ fibers, associated with temperature, pressure,
fast pain, and prickling itch sensations.
• 5 Hz: Activates unmyelinated C-fibers, involved in temperature perception, slow pain,
and burning itch sensations.
Ham et al. analyzed the relationship between the frequency of response at each sensation
(stinging, burning, and itching) during a lactic acid sting test and the CPT value of each
LAST with functional magnetic resonance imaging (fMRI) may allow a more objective
assessment 19 however, this approach is not feasible for routine use. In any case, a discrepancy
exists between the lactic acid response and the self-perception of sensitive skin.20 Therefore,
it is recommended to combine LAST with a concurrent questionnaire.16
CAPSAICIN TEST
The capsaicin test was more recently introduced to assess the hyperactivation of Transient
Receptor Potential Vanilloid 1 (TRPV1) in individuals with sensitive skin.21 TRPV1 is
a cationic ion channel activated by heat and capsaicin. In this test, a 0.075% capsaicin
emulsion is applied, and similar to the LAST, it relies on a subjective individual pain scale
for evaluation.
Interestingly, the Capsaicin Detection Threshold (CDT) test combines the specific reactivity
of sensitive skin to capsaicin, the simplicity of the LAST application, and a threshold
detection method. Unlike traditional methods, it no longer quantifies the intensity of the
response but instead determines detection thresholds for topically applied capsaicin. The
test uses five capsaicin concentrations in a 10% ethanol aqueous solution: (3.16 × 10−5%,
1 × 10−4%, 3.16 × 10−4%, 1 × 10−3%, 3.16 × 10−3%).21 The method used to attain the
detection threshold consists of applying increasing concentrations of capsaicin onto the
nasolabial folds (with a 3-minute interval between each application). The vehicle is
simultaneously applied following a split-face, single-blind plan. The test is stopped as soon
as the subject reports a specific sensation on the capsaicin side.
NEUROPHYSIOLOGICAL TECHNIQUES
These methods are used for studying the impairment of somatosensory function in
neurologic diseases. They are based on different stimuli: thermal (cold, warm), electrical,
or mechanical. Their use is more restricted to specialized centers, and they are rarely used
to assess sensitive skin.
CURRENT PERCEPTION THRESHOLD (CPT)
Sensitivity evaluations using the Current Perception Threshold (CPT) method distinguish
between types of nerve fibers based on their activation by three different current frequencies,
facilitated by the Neurometer® CPT® device (Neurotron Inc., Aurora, CO, USA).
Transcutaneous electrical stimuli are delivered through two electrodes. The frequencies
produced by the Neurometer® CPT® selectively stimulate three subsets of nerve fibers:
• 2000 Hz: Activates large myelinated Aβ fibers, responsible for touch and pressure
sensation.
• 250 Hz: Activates small myelinated Aδ fibers, associated with temperature, pressure,
fast pain, and prickling itch sensations.
• 5 Hz: Activates unmyelinated C-fibers, involved in temperature perception, slow pain,
and burning itch sensations.
Ham et al. analyzed the relationship between the frequency of response at each sensation
(stinging, burning, and itching) during a lactic acid sting test and the CPT value of each
