INTRODUCTION
Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by intense pruritus and recurrent eczematous lesions. Although it most often begins in infancy and affects up to 30% of children, it is also highly prevalent in adults [1]. Recent observations suggest, the late-onset AD occurs more frequently than previously believed [2]. The pathophysiology of AD is complex and multifactorial, involving skin barrier dysfunction leading to increased permeability, alterations in cell-mediated immune response, transepidermal water loss, IgE mediated hypersensitivity and environmental factors [1, 3].
Nonspecific local and systemic immunosuppressive agents, such as glucocorticosteroids and calcineurin inhibitors are commonly used in AD treatment. Biological therapy plays an increasingly important role in disease management, and numerous new agents are currently under investigation [4]. Dupilumab, which inhibits IL-4 and IL-13 signaling, is the first biologic therapy approved for the treatment of AD [5].
Pruritus is one of the most common and burdensome symptom in patients with inflammatory skin diseases, particularly in AD [6]. It has been shown in multiple studies to significantly impair quality of life [7]. The itch–scratch cycle perpetuates inflammation: scratching worsens inflammation, which further activates nerve fibers and intensifies the sensation of itching [8].
It is well established that skin cooling can relieve pruritus [8, 9]. Consequently, patients are frequently advised to avoid hot baths, as both heat and sweat are known to aggravate AD symptoms [10].
However, previous observations, careful investigation of our patients and several medical interviews have led us to the hypothesis that some patients intentionally use hot water in order to alleviate or diminish pruritus. Additionally, a few patients even reported to use a flow of hot air from a hair dryer to get instant relief. Despite acknowledging that these practices may worsen skin condition in the long term, patients described the instant relief as difficult to resist. These preliminary insights prompted us to design a survey aimed at evaluating the frequency of this phenomenon among individuals with AD. Our preliminary observations prompted us to create a survey to estimate frequency of this phenomenon among AD patients.
OBJECTIVE
The main purpose of this study was to evaluate the prevalence of using hot water or hot air among patients with AD as a method to relieve pruritus. Additionally, we aimed to establish effects, consequences and connection of the habit to any of disease-related aspects such as medication, severity or onset of the disease.
MATERIAL AND METHODS
This study included a total of 158 individuals diagnosed with AD and was available for 30 days; participation was voluntary. AD who participated in the online survey. The survey was published in the online support group dedicated to adults with AD and was available for 30 days; participation was voluntary. The questionnaire included 17 one- and multiple-choice questions about duration of the disease, severity of symptoms, medications and several aspects of use of hot water or hot air. Participants could skip questions they did not want to answer.
The Independent Bioethics Committee for Scientific Research deemed that formal approval was not required since the study uses completely anonymized data and does not involve patient contact.
Statistical analysis
The data from this study were analyzed using Microsoft Excel 2010 and Statistica software, version 13.0 (StatSoft, Poland). Quantitative variables were expressed as means with standard deviations (SD) and percentages for each group (%). Qualitative variables were expressed as absolute numbers and percentages.
To evaluate the statistical significance, contingency tables for variables compared were made. Then, depending on the sample size, tthe following tests were applied: Pearson’s χ2 test, Yates’ correction test, or Fisher’s exact test (used in cases of low cell counts) to assess associations between qualitative variables. When comparing two groups for quantitative data, Student’s t-test was used. The threshold for statistical significance in this study was set at p < 0.05.
RESULTS
Out of 158 participants, 142 were women (89.9%) and 16 were men (10.1%). Based on age, participants were divided into 5 groups: below 18 years old – 12 (7.6%) subjects, between 18 and 25 years – 69 (43.7%), between 26 and 35 years – 53 (33.5%), between 36 and 45 years – 18 (11.4%), and above 45 years old – 6 (3.8%) individuals.
Eighty-two (51.9%) participants reported suffering from AD since infancy, 30 (19%) were diagnosed during childhood, 14 (8.9%) developed AD at puberty, and 32 (20.3%) in adulthood.
To establish approximate severity of AD we asked about subjective feeling of disease severity and divided participants into 3 groups: mild AD – 17 (10.75%) patients, moderate AD – 99 (62.65%) patients, and severe AD – 42 (26.6%) patients.
In the survey, 94.9% of respondents reported using some form of topical therapy for AD. Out of 158 participants, 125 (79.1%) used emollients, 102 (64.6%) – steroid ointments, (12%) 19 – calcineurin inhibitors, 15 (9.5%) – antibacterial and antifungal ointments, whereas 7 (4.4%) claimed not to use any topical therapy. In addition, 97 (61.4%) patients reported the use of systemic therapies, including antihistamines (81; 51.3%), cyclosporine A (9; 5.7%), and oral glucocorticosteroids (17; 10.8%). Other types of systemic therapies, such as tralokinumab, baricitinib, or abrocitinib, were reported by 6 patients (3.8%).
When patients were asked whether they had ever used hot water to alleviate symptoms such as itching, pain, or burning, 99 (62.7%) respondents answered affirmatively, while 59 (37.3%) denied ever having done so. Regarding the methods of hot water application, 53 (53.5%) reported using hot tap water at the highest available temperature, 34 (34.3%) reported taking hot baths to relieve itching, and 12 (12.1%) indicated using both methods. In response to a question about using hot air (e.g., from a hair dryer) to relieve AD symptoms, 32 (20.3%) participants responded positively, whereas the remaining 126 (79.7%) reported never using this method.
Out of 105 respondents, who confirmed having used hot water and/or hot air, 19 (19.1%) could see and feel subjective improvement of lesions, whereas 86 (81.9%) deny seeing any improvement. Regarding the question if using hot water or hot air causes worsening of symptoms, 78 (74.3%) respondents confirmed that the skin condition gets worse after using hot water or hot air. Thirty-three (42.3%) individuals can see the worsening straight away after the stimulus, 36 (46.2%) within up to an hour, and 7 (9.0%) could see the worsening several hours later.
Interestingly, 55 (52.4%) out of 105 participants who confirmed having used hot water and/or hot air regretted using hot water or air, whereas 28 (26.6%) did not regret it, and 22 (21%) did not think about it.
Another section of the questionnaire aimed to assess the feelings and sensations associated with using hot water or hot air. Surprisingly, 76 (72.4%) respondents reported experiencing relief, excitement, and pleasure when using hot water or air, while 29 (27.6%) denied experiencing any relief.
We asked participants to rate the average level of pleasure experienced at the time of exposure to the stimulus. Patients were instructed to select how pleasurable the hot water felt on a scale from 0 to 10. A score of 10 was selected by 22 respondents (20.1%), 9 by 19 (18.1%), 8 by 22 (20.1%), 7 by 12 (11.4%), 6 by 7 (6.7%), 5 by 4 (3.8%), 4 by 1 (1%), 3 by 2 (1.9%), 2 by 2 (1.9%), 1 by 5 (4.8%), and 0 by 9 (8.4%) (fig. 1). All survey questions and corresponding responses are presented in table 1.
Table 1
Nine survey questions regarding the use of hot water or hot air and corresponding responses
| Have you ever used hot water to relieve symptoms of AD (itch, pain, burning of the skin)? 158 answers | ||||||||||
| Yes | No | |||||||||
| 99 (62.7%) | 59 (37.3%) | |||||||||
| In what way have you used hot water to alleviate itch, pain, or burning sensations of the skin? 99 answers1 | ||||||||||
| Hot baths | Running tap water | Both methods | ||||||||
| 34 (34.3%) | 53 (53.5%) | 12 (12.1%) | ||||||||
| Have you ever used hot air to relieve symptoms of AD (itch, pain, burning of the skin)? 158 answers | ||||||||||
| Yes | No | |||||||||
| 32 (20.3%) | 126 (79.7%) | |||||||||
| Have you noticed improvement of skin lesions after using hot water or hot air? 105 answers2 | ||||||||||
| Yes | No | |||||||||
| 19 (18.1%) | 86 (81.9%) | |||||||||
| Have you noticed worsening of the skin condition after using hot water or hot air? 105 answers2 | ||||||||||
| Yes | No | |||||||||
| 78 (74.3%) | 27 (25.7%) | |||||||||
| How long after using the stimulus have you noticed the worsening? 78 answers3 | ||||||||||
| Right away | After up to 1 hour | After a few hours | After a longer period of time | |||||||
| 33 (42.3%) | 36 (46.2%) | 7 (9%) | 2 (2.5%) | |||||||
| Did you regret using hot water or hot air? 105 answers2 | ||||||||||
| Yes | No | I have never thought about it | ||||||||
| 55 (52.4%) | 28 (26.6%) | 22 (21%) | ||||||||
| Have you noticed that using hot water or hot air gives a feeling of pleasure, excitement or relief? 105 answers2 | ||||||||||
| Yes | No | |||||||||
| 76 (72.4%) | 29 (27.6%) | |||||||||
| Rate on the scale from 0 to 10 the level of pleasure, excitement, relief during the stimulus of hot water or hot air. 105 answer2 | ||||||||||
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| 9 (8.6%) | 5 (4.8%) | 2 (1.9%) | 2 (1.9%) | 1 (1%) | 4 (3.8%) | 7 (6.7%) | 12 (11.4%) | 22 (20.1%) | 19 (18.1%) | 22 (20.1%) |
Figure 1
Distribution of responses to the question: “Rate on a scale from 0 to 10 the level of pleasure, excitement, and relief experienced during exposure to hot water or hot air”
Gender, age, severity and onset of AD
Age of patients seems to be correlated with the use of hot water (p < 0.0015). In the age groups 18–25, 26–35, 36–45, the mean percentage of people who used hot water was about 70%. In contrast, most of participants under the age of 18 have never used this method (91.7%) and the participants over 45 years old also used it less often (50%). It seems that using hot air (for example from a hair dryer) is not correlated with age. However, nobody over 45 years old has ever used this modality.
It seems that the age of AD onset does not correlate with the tendency to use hot water or hot air to relieve symptoms. However, it can be observed that the later the onset age of AD, the lower the percentage of individuals who use these methods (p = 0.11).
There was no significant association between gender and the use of hot water or hot air; however, it should be noted that only 16 participants in the study were men.
In our study, the subjective severity of AD did not appear to correlate with the tendency to use hot water or hot air. However, this finding is limited by the fact that the survey was anonymous and no objective measure of AD severity was employed.
Therapy and medications
Most of the participants who use emollients in the therapy of AD have never used hot air to relieve symptoms (84%). Patients using cyclosporine A were prone to use hot air more often (55.6%) than those without cyclosporine A (18.1%) (p = 0.02). There was also a tendency in the group of cyclosporine A using patients to use hot water more often (p = 0.09) and only one of them has never used hot water to reduce symptoms of AD.
Use of other medications (both topical and oral) does not appear to correlate with the use of hot water or hot air among AD patients.
Level of excitement
There is a clear association between the mean level of pleasure experienced during the stimulus and the tendency to use hot water (p < 0.001) (fig. 2). Participants who admit to using hot water to ease itching reported a mean pleasure score of 7.1 points. In contrast, those who do not use this method for itch relief reported a mean pleasure level of 2.6 points.
DISCUSSION
At present, the specific mechanisms underlying pruritus in AD remain unclear [11]. Although histamine has long been recognized as a primary factor, recent evidence suggests that multiple additional mechanisms must be considered. In the literature, studies describe both histamine-dependent and non-histamine-dependent mechanisms of pruritus. The histaminergic pathway, with a special role of two receptors: H1 and H4, also includes PLCβ3 and PLA. Their interaction with these receptors leads to activation of the downstream target transient receptor potential vanilloid 1 (TRPV1) [11]. Activation of TRPV1 by histamine receptors facilitates the scratching response to histamine [11, 12]. The signal is conveyed by C-type fibers (CMi), which transmit it to the central nervous system. Histamine-independent pathways have been considered important because chronic refractory itch is often resistant to antihistamine therapies [11]. This pathway is mediated by a class of mechanically sensitive C-type fibers (CMHs), whose endings are primarily located in the epidermis [13]. CMHs can be stimulated by cowhage (a tropical leguminous plant), whose active substance is mainly the 36 kDa cysteine protease mucunain, which activates PAR2 and PAR4 receptors [11]. A similar effect has been demonstrated for other pruritogens such as chloroquine. Studies show that the transient receptor potential (TRP) cation channel is the downstream target of this pathway and can be activated by PAR2 [11, 14]. TRP family members that are activated by warm (TRPV2, TRPV3, and TRPV4) or cold (TRPM8 and TRPA1) temperature ranges are involved in the modulation of pruritus [15].
Sanders et al., in their study, presented modulation of itch by localized skin warming and cooling. In some cases, but not all, temperature-sensitive channels were involved. The authors suggest that innocuous temperature regulation of different pruritogens is complex and cannot be fully explained by vasomotor changes or TRP channel signaling in sensory neurons [16].
Correlation between using hot water or hot air and the mechanisms of pruritus is not clear. To our knowledge, this is the first study showing that high temperature may have a short-term relieving effect on pruritus in AD patients. None of up-to-date data on histamine, TRP channels or any other pruritogens explain why there seems to be a border between the temperature that stimulates itching and the point of temporary pleasure and relief. Mild burn of the skin may be a factor that blinds the pruritus for a short period of time. Another possible explanation could be the exhaustion of mediators in nerve fibers after exposure and their gradual replenishment thereafter, which corresponds to the fact that most participants experience worsening symptoms immediately or within an hour after using hot water or air. Then, the effect of vasodilatation and destruction of epidermis might lead to worsening of the skin condition what causes patients to regret. What draws attention is that the study demonstrates that despite 77% of respondents reporting worsening of symptoms following this method, patients nevertheless continue to resort to it during episodes of pruritus. Furthermore, the references observation that patients receiving cyclosporine A are more likely to use hot water or hot air suggests that the severity of AD may influence this behavior. However, more advanced studies involving dermatological examination are required since this study was based only on subjective feelings of severity of the patients. Another limitation of the study was the fact that the participants were an anonymous group of patients of an online support group who could voluntarily take part in the survey. This caused that only 16 participants were men.
CONCLUSIONS
Pruritus (itch) is one of the most common symptoms in patients with inflammatory diseases. Numerous therapies for AD are aimed at symptom reduction. Although warmth is known to exacerbate itching, this study demonstrates that exposure to maximum heat from tap water or hot air from a hair dryer is a commonly employed method among AD patients to alleviate pruritus, albeit often only transiently. It often results in regret and exacerbation of skin lesions. It is important to take this into consideration when studying the impact of temperature in AD patients, and it is hoped that this study will encourage further research on the topic. Moreover, raising awareness among patients with AD regarding the detrimental effects of this method may be crucial.
