Arguments for neuropathic pain in sensitive skin

Sensitive Skin Syndrome: A Low-Noise Small-Fiber Neuropathy Related to Environmental Factors?

Background and Objectives

Patients frequently complain of mild, transient, unpleasant skin sensations that cannot be diagnosed as common neuropathies. Dermatologists have termed these symptoms “sensitive skin syndrome.” This narrative review was performed for a better knowledge by other specialists.

Databases and Data Treatment

Publications on pain in sensitive skin syndrome were obtained from PubMed.

Results

There is a growing body of data supporting the concept that sensitive skin is a type of small-fiber neuropathy. The arguments are based on clinical data, a decrease in intra-epidermal nerve fiber density, quantitative sensory testing abnormalities and an association with irritable bowel syndrome and sensitive eyes. Sensitive skin is triggered by environmental factors. Sensitive skin is a frequent condition, with a lifetime prevalence of ~50% according to self-reports.

Conclusions

Mild levels of skin pain or itch are frequently experienced by patients, who rarely report them. There is a need for a better knowledge of sensitive skin because it can be the first level of small-fiber neuropathies.

Sensitive skin: A relevant syndrome, be aware

Sensitive skin is clinically defined by characteristic sensory perceptions including tightness, abnormal stinging, burning, tingling, pain and pruritus. Facial erythema may occur, and other body areas can be involved. Sensitive skin affects extremely the quality of life. According with the International Forum for the Study of Itch (IFSI), sensitive skin is defined as a syndrome. The unpleasant sensations described are in response to stimuli that normally should not provoke such sensations. Moreover, these unpleasant sensations cannot be explained by any skin disease. Sensitive skin is always considered when any new consumer health, cosmetic or household product is introduced in the market. Once sensitive skin is recognized, it is mandatory to identify specific triggers that commonly induce symptoms and even cutaneous visible signs. Sensitive skin syndrome can be exacerbated by an allergic setting and environmental factors (cold, hot, dryness, pollution, wind, chemicals ...), a source of intolerance and unpleasant sensations. Cosmetics are the main triggering factors of sensitive skin according to patient's reports. The presence of potentially irritant substances in their composition increases the clinical expression of symptoms. As sensitive skin is frequent, and it is increasing based on the current development of cosmetic use worldwide, there is a need to develop better skin care products. The continuous research of active and safe skin care products to prevent and treat sensitive skin is extremely welcome.

Sensitive Skins May Be Neuropathic Disorders: Lessons from Studies on Skin and Other Organs

Sensitive skin can be considered a neuropathic disorder. Sensory disorders and the decrease in intra-epidermal nerve ending density are strong arguments for small-fiber neuropathies. Sensitive skin is frequently associated with irritable bowel syndrome or sensitive eyes, which are also considered neuropathic disorders. Consequently, in vitro co-cultures of skin and neurons are adequate models for sensitive skin.

Prevalence and Severity of Dermatological Condition-Associated Skin Pain in the Chinese

BACKGROUND/AIM

Although the characteristics of cutaneous sensory symptoms in the general population have been documented, dermatological condition-associated skin pain has not been characterized yet. In the present study, we aimed to characterize dermatological condition-associated skin pain in the Chinese.

SUBJECTS AND METHODS

A questionnaire was given to outpatients to identify self-proclaimed skin pain at our dermatology clinic. The severity of skin pain was assessed using pain scale 0-10. Prevalence and pain severity were compared between males and females.

RESULTS

A total of 2144 patients, including 1254 females and 890 males aged 13-94 years, were included in this study. The overall prevalence of skin pain was 9.93% in this cohort. The prevalence of skin pain varied greatly with dermatological conditions (p<0.0001). Moreover, a higher prevalence of skin pain was observed in males than in females (p<0.05). Among the dermatological conditions reported, higher skin pain scales were found in subjects with either glucocorticoid-induced dermatitis (4.20 ± 0.73) or herpes zoster (4.00 ± 0.29). While the overall pain scales were comparable between males and females (2.38 ± 0.13 versus 2.68 ± 0.13), pain scales in patients with eczematous dermatitis were higher in females than in males (p<0.05). Furthermore, pain scales correlated positively with age. However, pain scales did not differ between subjects with versus without a family history of cutaneous sensory symptoms. These results demonstrate that the prevalence and severity of dermatological condition-associated skin pain vary with dermatological conditions and gender in the Chinese.

CONCLUSION

Patients with some dermatological conditions may experience skin pain. Although the pain is moderate, it can negatively impact the quality of patients' lives. Alleviation of skin pain should be considered when treating patients with certain dermatological conditions.

Itch Processing in the Skin

Itching can result from activity of specialized primary afferent neurons (“pruriceptors”) that have been shown to express certain molecular markers such as B-type natriuretic peptide and several members of the Mrgpr-family in rodents. On the other hand, neurons involved in pain processing (“nociceptors”) can also provoke itching when the activation site is restricted to an isolated tiny spot within the epidermis. Individuals classified as having sensitive skin report increased itching and pain sensations upon weak external stimuli that are not painful or itchy in the control group. Numerous possible factors could contribute to sensitive skin along the pathway of transduction of the external stimuli into peripheral neuronal signals, followed by neuronal processing, finally resulting in the perception: (a) reduced local protective factors leading to impaired skin barrier function, (b) increased production of excitatory skin mediators, (c) sensitized peripheral neurons, (d) facilitated spinal and central processing, and (e) reduced descending inhibition from the central nervous system. For all of those pathophysiological mechanisms there are clinical examples such as atopic dermatitis (a,b,c), neuropathic itching (c,e), and restless leg syndrome (d,e). However, none of these factors have been directly linked to the occurrence of sensitive skin. Moreover, individuals reporting sensitive skin are heterogeneous and a subpopulation with defined pathophysiology has not yet been identified. Given that the condition is reported in about 50% of women, and thereby includes many healthy individuals, it appears problematic to assign a definitive pathophysiological mechanism to it.

Sensitive skin

Sensitive skin is a clinical condition defined by the self-reported facial presence of different sensory perceptions, including tightness, stinging, burning, tingling, pain and pruritus. Sensitive skin may occur in individuals with normal skin, with skin barrier disturbance, or as a part of the symptoms associated with facial dermatoses such as rosacea, atopic dermatitis and psoriasis. Although experimental studies are still pending, the symptoms of sensitive skin suggest the involvement of cutaneous nerve fibres and neuronal, as well as epidermal, thermochannels. Many individuals with sensitive skin report worsening symptoms due to environmental factors. It is thought that this might be attributed to the thermochannel TRPV1, as it typically responds to exogenous, endogenous, physical and chemical stimuli. Barrier disruptions and immune mechanisms may also be involved. This review summarizes current knowledge on the epidemiology, potential mechanisms, clinics and therapy of sensitive skin.

A model for perception-based identification of sensitive skin

BACKGROUND

With high prevalence of sensitive skin (SS), lack of strong evidence on pathomechanisms, consensus on associated symptoms, proof of existence of 'general' SS and tools to recruit subjects, this topic attracts increasing attention of research.

OBJECTIVE

To create a model for selecting subjects in studies on SS by identifying a complete set of self-reported SS characteristics and factors discriminatively describing it.

METHODS

A survey (n = 3058) was conducted, comprising questions regarding socio-demographics, atopy, skin characteristics, personal care, degree of self-assessed SS and subjective and objective reactions to endogenous and exogenous factors. Exploratory factor analysis on 481 questionnaires was performed to identify underlying dimensions and multivariate logistic regression to find contributing variables to the likelihood of reporting SS.

RESULTS

The prevalence of SS was found to be 41%, and 56% of SS subjects reports a concomitant atopic condition. The most discriminative were the eliciting factors toiletries and emotions, and not specific skin symptoms in general.

CONCLUSION

Triggers of different origins seem to elicit SS, it is not defined by concomitant skin diseases only, suggesting existence of 'general' SS. A multifactorial questionnaire could be a better diagnostic than a one-dimensional provocative test.