The Brain-Skin Nexus

By Ram Rao, Ph.D., Principal Research Scientist for Apollo Health

Generally, we consider the brain as that ‘thing inside the skull far away from the body,’ so a close nexus between the brain and skin seems far-fetched and ridiculous. In reality, the brain-skin nexus gets established early on during the formation of an embryo. One of the three primordial structures in the young embryo, termed the ‘ectoderm,’ differentiates into the brain and skin. Thus, it appears reasonable to speculate that the brain and skin may be connected since they arise and differentiate from the same primordial entity. Now evidence-based research supports the brain-skin nexus.

The skin insulates the entire body guarding it against extreme temperatures, harsh sunlight, toxic pollutants, and chemicals. It protects the body from persistent infection and is a site of synthesis of vitamin D (Vit D), also known as the ‘sunshine vitamin.’ Evidence-based research studies suggest a close relationship between Vit D deficiency and Alzheimer’s disease (AD)-associated cognitive decline. Vit D plays an important role in brain health and exerts various neuroprotective effects in brain areas essential for cognition. Low levels of Vit D are associated with a more than twofold increased risk of developing dementia. Vitamin D deficiency is common among older adults, partly because the skin’s ability to synthesize Vit D decreases with age.

Furthermore, as the largest external organ, another important function of the skin is to perceive the sense of touch. Thanks to the skin, we can experience variations in temperature, pressure, and pain. The skin is densely packed with nerve cells and constantly communicates with the brain. This sensory stimulation is what causes you to offer a handshake, reach out for a hug, or even fight back. Have you ever noticed how a bear hug calms you down or how a simple massage leaves you smiling and feeling relaxed? During a body massage, slow nerve fibers on the skin communicate with the brain to lower the stress hormone cortisol and increase the love hormone oxytocin, which triggers an overall positive feeling. Thus, gentle massage therapy certainly benefits the skin, and keeping the skin healthy benefits the brain as well. While cause and effect can be difficult to ascertain, research studies show that the skin reacts to mental stress by activating the body’s defense systems. Mental stress can negatively impact skin structure and function, pointing to the close nexus between the skin and the nervous system. Thus, it appears that anything that affects the brain may affect the skin and vice-versa.

Not surprisingly, scientists are proposing a skin test for detecting brain conditions, including Parkinson’s (PD) and AD. The presence of certain brain-associated proteins in the skin in disorders like PD and AD led researchers to believe that the skin is a good candidate for diagnosing these brain conditions. In a study involving sixty-five volunteers, twelve of whom were healthy and the remaining 53 who had PD, AD, or another type of dementia, scientists collected skin biopsy samples to test for the presence of two abnormal proteins, tau, and alpha-synuclein. To their surprise, the twenty people with AD and the sixteen with PD had elevated levels of both tau and alpha-synuclein in their skin compared to the healthy controls and the patients with other types of dementia. While additional research is needed to confirm these results, the findings are certainly exciting because skin biopsies could be tested from patients that are in the early stage of the disease. The work points to a possible diagnostic test that would be minimally invasive and could provide an earlier and more accurate diagnosis.

The brain-skin nexus appears so strong and reliable that a medical subspecialty called psychodermatology has been established that primarily treats skin disorders using psychological and psychiatric techniques. While we await more research and mechanistic studies to confirm the brain-skin nexus, the results thus far suggest that one of the pathways to the brain starts at the skin.