Acupuncture for the Treatment of Itch: Peripheral and Central Mechanisms

# Acupuncture in the Treatment of Itch: A New Scientific Perspective

Itch is an uncomfortable sensation that provokes the desire to scratch, representing one of the most distressing symptoms for patients and a considerable clinical challenge for physicians. This sensation can result from dermatological diseases such as psoriasis, urticaria, and eczema, or from systemic conditions such as end-stage renal disease or primary biliary cirrhosis. European studies show that the incidence of itch in dermatological diseases reaches 54.5%, while in the healthy population it is only 8%. In Brazil, although we do not have specific data mentioned in the study, the situation probably reflects patterns similar to those observed internationally.

The impact of chronic itch on quality of life is substantial, affecting emotions, attention, eating habits, sexual function, and sleep. The longer the duration and severity of the itch, the greater its negative impact on work productivity and daily activities. Some patients may develop psychosocial comorbidities, including anxiety, depression, and even suicidal tendencies. Despite advances in drug development, clinical control of itch symptoms remains challenging, as the underlying biological mechanisms are not yet fully understood.

A comprehensive scientific review examined the efficacy of acupuncture in the treatment of itch, analyzing both clinical studies and neurobiological mechanisms. The objective was to understand how acupuncture relieves itch through peripheral and central mechanisms, providing a scientific basis for further research. The methodology involved analysis of randomized clinical trials and experimental studies that investigated everything from cellular receptors to brain activity, using techniques such as functional magnetic resonance imaging and molecular analysis.

Clinical results demonstrated that true acupuncture was significantly superior to sham acupuncture in reducing itch scores and improving quality-of-life indices. Studies with atopic dermatitis patients showed significant reductions in the SCORAD index (a scale that assesses dermatitis severity) and on the visual analog scale for itch. In patients with uremic pruritus during hemodialysis, acupuncture produced lasting relief, maintaining benefits for up to three months after treatment. The most used acupuncture points included Quchi, Zusanli, and Xuehai, applied through manual techniques, electroacupuncture, or acupressure.

The mechanisms of action proved to be complex and multifaceted. In acute itch, acupuncture acts on mediators such as serotonin and its receptors, which are important for the transmission of histamine-independent itch signals. In animal models, the technique effectively reduced mast cell degranulation and decreased serum serotonin concentrations. In the central nervous system, acupuncture decreased the activity of serotonergic neurons in the medulla oblongata, reducing the excitability of nerve cells.

In humans, MRI studies showed that positive functional connectivity between the putamen and posterior middle cingulate cortex was associated with the antipruritic effects of acupuncture.

For chronic itch, the mechanisms involve regulation of cytokines released by immune cells. Electroacupuncture has been shown to reduce levels of interleukin-4 and interleukin-2 in the blood of patients with atopic dermatitis, while increasing interferon-gamma. The technique also intensified levels of the anti-inflammatory cytokine interleukin-10 in serum and inhibited tumor necrosis factor-alpha, resulting in reduced skin inflammation. In the central nervous system, acupuncture suppressed microglial activation in the spinal cord, a process known to exacerbate itch sensations via the p38 MAPK signaling pathway.

The clinical implications are promising for patients suffering from acute or chronic itch. Acupuncture offers a safe therapeutic alternative with minimal side effects, especially valuable considering the limitations of conventional treatments. Antihistamines, widely used, frequently fail to control chronic itch and can increase the risk of falls in the elderly. Systemic corticosteroids, although effective, carry serious side effects limiting their prolonged use.

For health professionals, these results suggest that acupuncture may be integrated as adjunctive or primary therapy, especially in cases refractory to conventional treatments. The technique proved particularly effective when applied three times a week for four weeks.

However, some limitations should be considered. Research on the neurobiological mechanisms of antipruritic acupuncture, although promising, is still less in-depth compared with knowledge about the mechanisms of itch itself. There is a circadian variation phenomenon in itch, being generally more severe at night, but studies have not adequately explored how acupuncture interacts with these biological rhythms. In addition, chronic itch is often associated with psychopathologies such as anxiety and depression, and although acupuncture can improve itch through treatment of related mental illnesses, specific research in this area is still needed.

The studies analyzed varied in methodologies, sample sizes, and evaluation criteria, which may influence the generalizability of the results.

In conclusion, this review provides solid scientific evidence that acupuncture constitutes an effective and safe therapeutic option for acute and chronic itch. The mechanisms of action involve complex modulation of inflammatory mediators, neurotransmitters, and brain activity, offering multiple therapeutic targets. For future clinical application, a better understanding of the molecular and cellular mechanisms will be necessary, using advanced technologies such as in vivo calcium imaging, modern genetics, and neuroimaging tools to expand our knowledge about relevant circuits in the spinal cord and brain. Cytokines, endocannabinoids, opioids, and their receptors represent important targets that deserve special attention in future research, promising to further optimize this ancient therapeutic modality with a contemporary scientific basis.