How many times have we used the expression “skin deep” referring to emotions and moods? And how often have we been told that these are “all over your face”? In fact, our language contains some typical expressions emphasizing the connection between skin and brain, which is much more intense and complex than we might think. The skin is the largest organ we possess, separating us and at the same time allowing us to communicate with the outside world, the border organ between the “inside” and the “outside.” However, it functions as much more than a simple covering: recently, in addition to its barrier properties, scientific research has expanded characteristics that would allow us to consider it a “third brain” (Denda, 2015).

The relationship between skin and brain begins well before birth: the two organs originate from the same embryonic sheet, the ectoderm, which, during the first few weeks of gestation splits into the epidermis and central nervous system. Even once they have split, however, the two organs remain connected for life, and we further understand the mechanisms and reasons for this close connection. To date, the skin is considered a neuroendocrine organ (Slominski et al., 2012) by virtue of its ability to recognize, discriminate and integrate different signals coming from inside and outside while maintaining our body’s balance (homeostasis), and it is able to communicate with the nervous, endocrine and immune systems. Skin cells, keratinocytes in particular, produce and respond to the same neurotransmitters present in the central nervous system, and possess systems for detecting thermal, mechanical and chemical stimuli as well as secreting hormones and neurohormones capable of influencing the body’s state along with our emotional states (Denda et al., 2013). It is also believed that the skin has its own peripheral equivalent of the hypothalamus-pituitary-adrenal axis (Martins et al., 2020), that is, the system that regulates responses to stress.

This is why the connection between skin and brain explains many cutaneous manifestations of our emotional states: dermatology, psychology and psychiatry form a cross-disciplinary field – psychodermatology – that deals with precisely this. But what is a psychodermatological disorder? It is defined as a condition that involves the interaction between skin and mental states (Koo et al., 2001), and, in particular, there are different types of manifestations that fall within this category, including psychophysiological disorders and secondary psychiatric disorders (ibid). While these are, in the first case, dermatological manifestations, they can arise or become aggravated by or in association with emotional states (e.g., psoriasis, atopic dermatitis, alopecia areata); the second case includes all those situations in which dermal manifestations have an effect on the subject’s psychological state (e.g., anxiety, depression, social and quality of life impairment). From this distinction, another notable aspect emerges: the relationship between skin and brain is two-directional, that it is not only the brain and our emotional states that influence the skin’s state, but also the latter that has an effect on our psychological state.


– M. Denda. Epidermis as the “third brain”? Dermatologica Sinica (2015).

– A. Slominski, et al. Sensing the environment: Regulation of local and global homeostasis by the skin neuroendocrine system. Advances in anatomy, embryology, and cell biology (2012).

– M. Denda et al. How does epidermal pathology interact with mental state? Medical Hypotheses (2013).

– A.M. Martins et al. The brain-skin connection and the pathogenesis of psoriasis: A review with a focus on the serotonergic system, Cells (2020).

– J. Koo, Psychodermatology: The Mind and Skin Connection, American Academy of Family Physicians (2001)


Dott.ssa Anna Marras

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