The skin and the brain stem from a common embryonic origin.
After fertilization and the multiple cell divisions that follow, the gastrula – composed of three germ layers – develops. One of its germ layers, the ectoderm, later differentiates into both the epidermis and the nervous system, beginning in the second trimester. Could this common origin result in a functional connection that is still relevant after birth? Research indicates that it does.
The ectoderm consists of columnar cells, which are, however, somewhat flattened or cubical toward the margin of the embryonic disk. It forms the whole of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, sudoriferous, and mammary glands, the hairs and nails, the epithelium of the nose and adjacent air sinuses, and that of the cheeks and roof of the mouth.
Henry Gray's Anatomy of the
Human Body (1918)
The epidermis and the brain have a structural resemblance.
Stratum Corneum
Lipid bilayers between corneocytes on the uppermost layer of the epidermis (stratum corneum) play key roles in preventing water loss and in blocking external pathogens, thus providing important epidermal barrier functions.
Transmission Electron Micrograph
Photo: Debra Crumrine
Myelinated Axon
The axon of a neuron is surrounded by myelin sheaths, composed of lipid bilayers, that act very much like electrical wires. These sheaths are crucial in rapid transmission of electric impulses. Because of their protective properties, we refer to them as Neuron Barrier™.
Transmission Electron Micrograph
Photo: Trinity College, Hartford CT
Hover over the images for a description of their structures.
The HPA Axis is one of the bridges that connect the skin and the brain.
The hypothalamic-pituitary-adrenal (HPA) axis is a key pathway through which the brain and the skin affect each other. Stress hormones in the HPA axis have been shown to worsen the symptoms of skin diseases, such as atopic dermatitis and psoriasis.¹ The skin has also been known to express neurotransmitters and hormones that regulate the HPA axis, such as serotonin and acetylcholine.² After all, it really does seem that the skin is the mirror of the soul.
Evidence suggests that certain features of psychiatric and skin disorders are closely related.
For instance, the profile of inflammatory molecules (pro-inflammatory cytokines) of those with autism is similar to the profile of those with atopic dermatitis.³ One study also showed that children with atopic dermatitis have a higher chance of being diagnosed with psychiatric disorders, such as autism, depression, and ADHD.⁴ Another longitudinal study indicated that children with atopic dermatitis are ten times more likely to have autism.⁵ The quest to find exact links between autism and atopic dermatitis is ongoing in the research community, as well as by our team.
1. Kim, J, et al. “Expression of Hypothalamic–Pituitary–Adrenal Axis in Common Skin Diseases: Evidence of Its Association with Stress-Related Disease Activity.” Acta Dermato Venereologica, vol. 93, no. 4, 2013, pp. 387–393., doi:10.2340/00015555-1557.
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2. Slominski, Andrzej, and Jacobo Wortsman. “Neuroendocrinology of the Skin.” Endocrine Reviews, vol. 21, no. 5, 2000, pp. 457–487., doi:10.1210/edrv.21.5.0410.
3. Theoharides, T C, et al. “Atopic Diseases and Inflammation of the Brain in the Pathogenesis of Autism Spectrum Disorders.” Translational Psychiatry, vol. 6, no. 6, 2016, doi:10.1038/tp.2016.77.
4. Yaghmaie, Pouya, et al. “Mental Health Comorbidity in Patients with Atopic Dermatitis.” Journal of Allergy and Clinical Immunology, vol. 131, no. 2, 2013, pp. 428–433., doi:10.1016/j.jaci.2012.10.041.
5. Lee, Chih-Ying, et al. “Longitudinal Association between Early Atopic Dermatitis and Subsequent Attention-Deficit or Autistic Disorder.” Medicine, vol. 95, no. 39, 2016, doi:10.1097/md.0000000000005005.