354 JOURNAL OF COSMETIC SCIENCE
interesting for the evaluation of skin irritation.5,6 The primary concern is that sensitive skin
is strongly linked to specific individuals, emphasizing the need for clinical evaluation.
A meta-analysis of 13 studies revealed that sensitive skin may be associated with various
factors, including cosmetics, physical triggers (such as temperature fluctuations, cold,
heat, wind, sun, air conditioning, and humidity levels), chemical agents (such as water and
pollution), and psychological factors (such as emotional stress). Among these, cosmetics
were identified as the most significant factor, far surpassing the others.7
To support cosmetic claims related to sensitive skin, panels of individuals with sensitive
skin are often used to demonstrate that cosmetic products do not worsen the condition and
may even improve it. However, many evaluations lack credibility due to the inadequate
definition of sensitive skin panels.
A sensitive skin panel must be defined by two criteria:
• Absence of skin disease: Sensitive skin cannot be accurately evaluated if it is unclear
whether the condition being assessed is sensitive skin, a skin disease, or a combination
of both.
• Clearly defined positive criteria: Specific and measurable criteria for assessing sensitive
skin must be established.
These criteria can be assessed with different methods, which will be cited in the following
paragraphs.
CHEMICAL TESTS
Stinging test remains the most commonly used technique to define sensitive skin panels.8
Many other objectification techniques have been proposed: chromametry, laser Doppler,
thermal sensitivity test, capsaicin test, sodium lauryl sulfate, dimethyl sulfoxide, ethanol
or other chemical compounds, etc.9–11 These tests try to evaluate the sensory and/or the
erythemal response of skin to some factors.
STINGING TEST
The famous lactic acid stinging test (LAST) of Frosch and Kligman is the first standardized
test.8 It consists of the application of 0.5 mL of 10% (or 5%) lactic acid to the nasolabial
fold with subsequent assessment of the severity of the subjective symptoms. Erythema
is sometimes evaluated. Control is provided by the application of a saline solution the
other fold.
Stinging test is commonly used and is very useful for the follow-up of sensitive skin.
However, it is a poor instrument to assess sensitive skin.12 Hence, Marriott et al. tested four
chemicals commonly used to induce different sensory effects: lactic acid (stinging), capsaicin
(burning), menthol (cooling), and ethanol (a combination of burning and stinging). They
observed significant variations in reactivity to the tested substances and found that increased
reactivity to one material did not reliably predict reactivity to others.13 An important intra-
individual variability was also observed comparing the responses to only two chemicals.14
Nonetheless, other authors found LAST was predictive of sensitive skin.15
Another controversy is the quantification of the intensity of unpleasant sensory responses.16,17
The semi-quantitative assessment is frequently used.18 Measuring cerebral responses to the

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