The Skin and Transcranial Direct Current Stimulation

Transcranial direct current stimulation, or tDCS, has become one of the fastest growing brain modulation tools, but beneath the electrodes is an often overlooked, critical part of the way tDCS works, the skin. tDCS is a non-invasive brain stimulation technique that works by applying low electrical currents to specific areas of your brain to stimulate activity.¹ This low current can modulate neuronal firing activity and is used for research in depression, working memory, attention, and even stroke rehabilitation.²  Though electrical stimulation dates back to the 19th century, its current accessibility, affordability, and low side effects have started to appeal to a larger audience.

Fundamentally, tDCS works through electrical currents. These low-level currents are delivered through electrodes on the scalp in two main ways: anodal and cathodal stimulation.³ Simply put, anodal stimulation increases neurons’ activity, primarily used to boost brain function; while cathodal stimulation does the opposite, decreasing activity and attempting to reduce brain activity in certain regions.⁴ Still, these differences are not seen in black and white, with one sometimes boosting the other.⁵ The effects depend heavily on factors such as baseline neural activity, stimulation intensity, duration, and the specific brain region being targeted, meaning that anodal and cathodal stimulation can sometimes produce overlapping or unexpected effects.⁶ Taking a step back, however, we have to realize that before the current has any effect on your brain, it has to first pass through the scalp. 

Today, the clinical and cognitive effects of tDCS are still mixed. In a meta-analysis of 69 tDCS studies, significant effects of both anodal and cathodal stimulation on working memory, inhibition, and theory of mind have been found.⁷ In clinical applications, studies found that repeated tDCS showed improvements in MMSE cognitive scores and reduced P300 latency compared with placebos. ⁸ Still, in studies involving older patients, a controlled trial found no significant benefit of tDCS in cognition, mobility, or anxiety compared with placebo.⁹

Researchers could consider electrode preparation and consistent skin contact (saline soak, cleaning, impedance checks) because poor contact increases the risk of skin irritation, which then leads to a change in electrical delivery. 

During treatment, skin-related conditions can directly influence psychological outcomes. For example, in a recent study done, it was noted that if participants feel itching or burning under the electrodes, it could greatly affect mood, attention, or task engagement, therefore messing with the cognitive results.¹⁰ Safety/tolerability reviews show that these sensations are common enough for them to influence how people behave during the studies. Further, for tDCS to consistently provide results, there are a lot of factors that come into play. One of the most important ones is skin impedance—heavily influenced by hydration, skin thickness, and hair, which act as barriers to electrical conduction. Variability in these properties can cause uneven current distribution and, therefore, bias the results.¹¹ On a broader scale, skin properties vary case by case, so that could partly explain the large discrepancies in cognitive effects between various studies.¹² To systematically get rid of as many possible biases, skin preparation should be a priority. According to an article from Dr. Liji Thomas, researchers could consider electrode preparation and consistent skin contact (saline soak, cleaning, impedance checks) because poor contact increases the risk of skin irritation, which then leads to a change in electrical delivery.¹³ 

Ultimately, tDCS is going to be a critical piece of advancement in future medical practices, whether it be in the lab through gathering clinical data or in the hospital for treatments. Still, it is important to realize that as skin is the initial barrier, it can affect safety, participant experience, and even data interpretation. Integrating dermatological awareness into future tDCS research will help strengthen both its validity and transparency. 

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1. Woods et al., tDCS Beginner’s Guide. https://pmc.ncbi.nlm.nih.gov/articles/PMC5702643/ 

2. Clarke et al., anodal vs cathodal effects on excitability/executive function. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0124182 

3. Clarke et al., anodal vs cathodal effects

4.  Clarke et al., anodal vs cathodal effect

5. Scapin G, et al. Tracking the Effect of Cathodal Transcranial Direct Current Stimulation https://www.frontiersin.org/articles/10.3389/fnins.2018.00319/full 

6. Woods et al., tDCS Beginner’s Guide.

7. Lv S, et al. A meta-analysis of the effects of tDCS https://pubmed.ncbi.nlm.nih.gov/39376507/ 

8. Zhang L, et al. Does Transcranial Direct Current Stimulation Affect Potential P300?  https://pmc.ncbi.nlm.nih.gov/articles/PMC11200963/ 

9. Carvalho-Lima R, et al. Efficacy of tDCS in older individuals: A randomized controlled trial. https://pubmed.ncbi.nlm.nih.gov/38137062/ 

10. Franke T, et al. Tolerability of Repeated Application of Transcranial Electrical Stimulation.  https://pmc.ncbi.nlm.nih.gov/articles/PMC5786157/ 

11. Datta A, et al. Minimal heating at the skin surface during transcranial direct current stimulation (tDCS). https://pmc.ncbi.nlm.nih.gov/articles/PMC5522650/ 

12. Datta A, et al. Minimal heating at the skin surface during transcranial direct current stimulation (tDCS).

13. Liji T, Transcranial Direct Current Stimulation Risks https://www.news-medical.net/health/Transcranial-Direct-Current-Stimulation-Risks

Psychodermatology at a Glance

Psychodermatology is a relatively new field of study that dives deeper into the interplay of mental health and skin disorders. The skin and brain originate from the same embryonic tissue, the ectoderm, and remain intricately linked throughout life through neural, hormonal, and immune pathways. Therefore, the mind can influence a multitude of conditions, including eczema, psoriasis, alopecia, and acne. The simplest way of psychology manifesting into physical results is the worsened mental health that these conditions bring. For example, alopecia, which results in the loss of hair, worsens confidence and, on a broader scope, worsens mental health. This leads to a cycle of negative psychology, directly resulting in worsening conditions. Since the early days, celebrated scientists such as Hippocrates and Freud have hypothesized that stress can directly affect mental health. Though their understandings were only fundamental, they have paved the way toward our modern understanding. The contemporary understanding is that, due to the embryological link between the brain and skin (ectoderm), there are multiple mechanisms of connection. Some are the neuroendocrine, immune, cellular, and oxidative/molecular mechanisms. 

Due to the embryological link between the brain and skin, there are multiple mechanisms of connection.

The neuroendocrine pathway is essentially there to say that when a person is experiencing stress, the hypothalamic-pituitary-adrenal (HPA) axis releases corticotropin-releasing factor (CRF), ACTH, and cortisol. These elevated levels of cortisol disrupt the skin barrier, delay wound healing, and can even prematurely shift hair follicles from the growth (anagen) phase to the resting (telogen) phase. Stress also alters immune balance, increasing pro-inflammatory cytokines like IL-6, IL-1β, and TNF-α. Not only can this worsen inflammatory skin diseases, but it can also trigger autoimmune reactions such as alopecia areata. In hair follicles, stress-related inflammation damages the hair follicles, leading to shedding and delayed hair regrowth.

Further research also shows that stress generates reactive oxygen species that damage DNA and proteins in hair and skin cells. With cortisol also reducing protective molecules like hyaluronan and proteoglycans, it promotes a weakened follicle structure and early regression of the hair cycle. Finally, with neurogenic and sensory signaling, this indicates that as the skin is rich in sensory nerves that release neuropeptides (substance P, CGRP, VIP, etc.) during stress, these chemicals can cause inflammation, blood vessel permeability, and stimulate immune cells, all of which negatively affect the hair follicle. This process, as previously mentioned, creates the cycle where stress sensations worsen inflammation, and so as visible symptoms increase, so does stress perception. 

One of psychodermatology’s biggest challenges is objectively measuring stress. However, this invites opportunities for further research to be done focusing not only on biochemical markers but also on understanding how personal perception of stress shapes physical outcomes. Currently, researchers measure it with both subjective and biological indicators. Psychologically, scales such as the Perceived Stress Scale and Hospital Anxiety and Stress Scale assess stress levels. Biologically, stress is measured by looking at HPA-axis markers, such as cortisol and inflammatory cytokines, which show that the neuroendocrine and immune pathways are on. Other scales further note heart rate variability and behavioral observations in an attempt to fully measure a person's stress. 

To fulfill a holistic assessment, psychodermatology is forced to take on a unique approach compared to traditional dermatology treatments. Instead of creams or medication, therapy and stress reducers come into play. Therapy for stress management, for example, has been shown to reduce flare-ups in conditions like acne and psoriasis. Studies have shown that approximately 30% of dermatology patients exhibit psychiatric and psychosocial disorders, significantly contributing to the overall disability associated with dermatoses. Additionally, high rates of suicidal ideation have been reported, with 8.6% of outpatients with skin conditions. 

Psychodermatology reveals how deeply connected the mind and body truly are. Stress and emotion are seen as being intangible, but they manifest biologically through hormones, immune responses, and inflammation that can fundamentally alter the health of our skin and hair. Still, as much as science explains the mechanisms,  the field also challenges medicine to look beyond the physical, emphasizing the importance of treating patients as whole beings. 

The Placebo Effect

It’s raceday. You need to set a new personal record by .5 seconds to make it to states. At higher levels, it's these precious milliseconds that matter most. Of course, there is an easier, guaranteed way to make that time. The first thing that comes to mind is probably PEDs, or performance-enhancing drugs. But, what if there was a way for similar results to occur without doing anything illegal? 

Then, a mysterious figure comes into view. He offers you a pill, saying that it will make you run faster. With the race about to start, you don’t even question if it’s legal and take it. So, you run, and are overjoyed when you see the time qualifying for states. Still, your heart feels heavy, so you go up to him to ask, “What was in that pill you gave me?” He responds, “It was just sugar”. The placebo effect occurs when a placebo—in this case, sugar—creates a beneficial effect, not due to the treatment itself, but because of the psychological belief in the treatment.

The placebo effect was first studied in the 20th century, during World War II. When morphine was starting to run low, American anesthesiologist Henry Beecher noted that wounded soldiers given saline—essentially salt water—instead of morphine, saw similar pain relief, simply because they believed that they were receiving a powerful drug. This phenomenon prompted deeper research into the mind’s ability to influence the body’s response to treatment. 

The placebo effect operates on expectation. When someone believes that a pill or treatment will improve their condition, whether it's for pain, anxiety, or even athletic performance, their brain often responds accordingly. Neurotransmitters like endorphins or dopamine may be released, physically changing how the body feels or functions. In sports, this physiological trick can translate into tangible performance improvements. Runners might shave off milliseconds, lifters might add extra reps, and fatigue might set in later than expected. All of this is due to the brain's belief in an edge that does not chemically exist. 

When placebos can have a surprising impact, they also raise ethical questions. Is it right to deceive someone, even if it's for their benefit? And how far can the placebo effect truly go? Obviously, you can’t sugar-pill your way to Olympic gold, but the belief that you can get better, faster, or stronger might just be enough to tip the scale in cut-throat situations.

In a world where the tiniest edge can make the biggest difference, the mind might be the most overlooked performance enhancer of all

Interestingly, some researchers are now studying open-label placebos, where people are told they’re receiving a placebo, yet still experience benefits. At first, this might seem counterintuitive, but it shows the profound impact of the mind-body connection. In sports, this could open doors to mental training methods that boost performance without violating any rules.  

In a world where the tiniest edge can make the biggest difference, the mind might be the most overlooked performance enhancer of all. Whether through traditional placebos or open-label versions, belief can sometimes be just as powerful as biology.  In competitive sports, where boundaries are strictly regulated, harnessing these effects through transparent, evidence-based methods, such as open-label placebos, could redefine the way we approach performance in sports. The effective use of placebos holds immense potential for the future of training and competition.