FIGURE 8.1 Practical approach to sensitive skin.
TABLE 8.1
Overview of Testing Methods for Sensitive Skin
|
Sensory Reactivity Tests |
Irritant Reactivity Tests |
Dermal Function Tests |
|
|
Goal |
To evaluate cutaneous neurosensory response to the application of different chemical substances, or physical stimuli |
To assess objective signs of skin irritation after the application of SLS or other known irritants |
To measure structural or physiological cutaneous changes after the application of topical irritants |
|
Tests |
• Self-assessment questionnaires • Stinging test: 10% lactic acid (or capsaicin, ethanol, menthol, benzoic acid) • Thermal sensation test (QST) • Evaluation of itching response • Washing and exaggerated immersion test |
Assessment of cutaneous irritation by the following: • Colorimetry (visual erythema) • Laser Doppler velocimetry (nicotinate test) • Electrical capacitance • Corneometry (skin hydration) • Reflectance |
Parameters evaluated: • TEWL (basal or dynamic desorption curves) • Cutaneous pH • Epidermal thickness (measured by US, OM, or CM) • Skin penetrability (measured by UV light) |
|
Advantages Disadvantages |
Fast and easy to perform Subjective, intraindividual variability, and lack of predictive value |
Objective and noninvasive Indirect measurement and specialized complex tools |
Quantitative and accurate Time consuming, specialized, and expensive |
Source: Primavera, G., and Beradesca, E., Int J Cosmet Sci, 27, 1–10, 2005; Piel, 28, Rodrigues-Barata, R., and Conde Salazar-Gómez, L., Sensitive skin, 520–530, Copyright (2013), with permission from Elsevier; Escalas-Taberner, J., González-Guerra, E., and Guerra-Tapia, A., Actas Dermosifiliogr, 102, 563–571, 2011.
Note: CM: confocal microscopy; OM: optical microscopy; QST: quantitative sensory test; US: ultrasonography.
Testing Methods
To evaluate and quantify the severity of sensitive skin objectively, reproducible and noninvasive tests are absolutely necessary. According to Farage et al. (22,23), testing methods can be divided into three main groups depending on the biophysical factor assessed: those that investigate neurosensory response (sensory reactivity tests), those that evaluate visible cutaneous signs of irritation (irritant reactivity tests), and those that measure structural and physiological parameters of the skin as a consequence of the irritant effect (dermal function tests) (24). Table 8.1 represents an overview of the currently available testing methods.
Sensory Reactivity Tests
Because almost half of patients with sensitive skin report uncomfortable symptoms without accompanying visible signs of inflammation, new tools of sensory testing have been increasingly utilized to provide definite information (13).
These methods evaluate cutaneous neurosensory response to the application of different chemical substances or other physical stimuli (7). Of them, the stinging test of Frosch and Kligman (25), which consists of the application of 0.5 mL of 10% lactic acid to the nasolabial fold with subsequent assessment of the severity of the subjective symptoms, has traditionally been considered to be the most suitable, fast, and easy to perform (26). However, nasolabial stinging seems to be a poor predictor of general skin sensitivity (27). Marriott et al. (27) tested four chemicals commonly used to induce different sensory effects (lactic acid, stinging; capsaicin, burning; menthol, cooling; and ethanol, a mixture of burning and stinging), reporting a high number of variations in reactivity to the tested substances and a lack of predictive value of increased reactivity among the different materials (27). In addition, an important intraindividual variability has been demonstrated comparing the responses to only two chemicals (28).
Irritant Reactivity Tests
Irritant reactivity tests measure objective signs of skin irritation after the application of a known irritant substance (13). They are based on the topical application of sodium lauryl sulfate (SLS), or other chemicals, followed by the assessment of cutaneous irritation through several procedures, such as colorimetry (visual erythema after the application of varying concentrations of methyl nicotinate or SLS to the forearm), laser Doppler velocimetry (vasodilatory effect following nicotinate test), electrical capacitance or corneometry (skin hydration), and reflectance (14).
These methods are suitable noninvasive tools to objectively quantify sensitive skin but may occasionally require robust specialized appliances.
Dermal Function Tests
These types of tests relies on the measurement of structural or physiological cutaneous changes after the application of topical irritants, such as SLS or others. TEWL, cutaneous pH, and epidermal thickness, measured by ultrasonography, optical microscopy, or confocal microscopy, as well as skin penetrability, assessed with UV light, are the parameters most commonly used (13,14,24).
Although dermal function tests are highly accurate quantitative methods, their use is mainly limited to the investigation field, as they are especially very time consuming and require expensive and specialized tools to be carried out in daily clinical practice (14,29,30).
TEWL assessment is the most frequent procedure performed to evaluate and quantify the function of stratum corneum (24). The basal evaluation of TEWL is able to measure preclinical disease without altering the underlying skin condition by a noninvasive estimation of water pressure gradient above the skin surface (13,24). Some studies have proposed a combined assessment of desorption curves of TEWL and plastic occlusion test to quantify the severity of sensitive skin objectively. Most investigators already prefer this new approach, as changes on skin barrier can be dynamically assessed (26,31).
Contact Tests
To conclude the diagnosing process of sensitive skin properly, Pons-Guiraud (12) recommends performing patch tests in order to find out any sources of allergic contact dermatitis and advise the patient accordingly. In addition to standard series, these patients should be tested with their own products of daily use and specific batteries that include the most common allergens present in cosmetic and personal care products (24,26). Likewise, open and repeated application tests must be performed before making a final diagnosis (32). When photoallergic contact dermatitis or contact urticaria is suspected, workup should include photopatch and hypersensitivity test type 1, respectively (14).
Other Evaluations
Finally, if the whole complementary exams do not reveal any underlying signs suggestive of sensitive skin, the patient should be referred to mental health care providers (14,24).
Conclusion
The high prevalence and complex physiopathological origin of sensitive skin represent a challenge for dermatologists who face an increasing demand for the management of this condition. Because the manifestations of skin sensitivity are mainly subjective and transient, symptoms self-reported by the patients through self-assessment questionnaires, along with an accurate clinical evaluation, remain the best methods of diagnosis. Developing standardized and reproducible testing methods that let physicians objectively quantify the severity of the disease to advise and treat patients properly remains a real need not yet covered.
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