The skin is the largest organ in the body. It may appear to be a superficial covering, but it possesses multiple functions and is fundamental to health.
Skin conditions are common, and it is important not to separate them from the skin as a functional organ. Where we see skin conditions such as eczema, rosacea, acne and psoriasis it is an indication of a further underlying dysfunction and should be treated as such.
The skin itself is both influenced by the excretion, detoxification, endocrine, and immune systems as well as the microbiome but at the same time it plays a fundamental role in the regulation of all of these.
The functions of the skin are many and varied. Read on to discover this most fascinating organ.
The skin’s role in excretion
The skin’s role in detoxification is an interesting one as it is a mechanism for waste product excretion and therefore is reliant on the other detoxification systems in the body, so as not to become overwhelmed. On the flip side of this, the skin is our external covering and therefore has a high exposure to environmental toxins.
So firstly, let’s look at toxin excretion. The majority of waste excretion is performed by the liver and kidneys and compared to this excretion via the skin is somewhat more passive.
Most waste is excreted via the sweat glands and consists mainly of water, salts (particularly sodium, potassium and chloride ion) lactic acid, and urea1. Potassium, urea, ammonia, and lactic acid concentrations are higher in sweat than in plasma, although these levels are also regulated to some extent by reabsorption in the ductal tubule of the sweat gland.
Additionally, the sebaceous glands secrete lipid-based substances including pheromones, some hormones and products that moisturise the surrounding skin2, there can also be modest amounts of lipid soluble waste products.
If other excretion mechanisms are inadequate, e.g., constipation is present, this encourages the potential for a greater number of substances to be excreted via the sweat or sebum through the skin. Excess levels of waste products on the skin may contribute to irritation, inflammation and oxidative stress. Encouraging adequate bowel motility as well as supporting gut, liver and kidney function is essential.
Sweat via the skin is an acknowledged excretory route for toxic metals
Along with essential minerals, sweat is an acknowledged excretory route for toxic metals. Heavy metals such arsenic, lead, cadmium and mercury have been shown to be present in sweat.3 There is some evidence that increasing sweating with sauna therapy, can increase the excretion of these heavy metals. Sauna bathing has shown multiple benefits to cardiovascular health, increased antioxidant systems, increased resistance to stress.4
It should be noted that often skin conditions worsen in the winter months. It is worth highlighting that our pores are not so open, and we sweat less during the winter, potentially reducing this excretion pathway. Saunas and exercise in the winter can be helpful for some people during this time.
The skin’s function in detoxification
The skin possesses its own detoxification and antioxidant systems. It has been shown that it can degrade, inactivate, and eliminate numerous xenobiotics and endogenous toxic compounds through metabolising enzymes, ROS-scavenging (antioxidants), and sweat glands5–7.
Studies have demonstrated that when vasodilation and sweating are inhibited (e.g., on grafted skin) there is a reduction in the skin’s ability to regulate oxidative stress.. There is also an accumulation of endogenous waste substances (e.g., cortisol, catecholamines, and cytokines) in the circulation of postburn patients, likely to be due to the inability to excrete substances via sweat and or sebum5.
Therefore, the skin is not just a passive mechanism of excretion but metabolically active in the process of biotransformation.
Disruption of skin integrity by the presence of skin conditions can exacerbate impairment of detoxification pathways potentially worsening symptoms. Hence, supporting the normal integrity of the skin is a fundamental aim for all skin condition.
The skin’s ability to detoxify is innately bound to the fact that it is exposed to so much. The robust detoxification and immune capabilities of the skin are fundamentally underpinned by its microbiome.
The skin possesses its own specific microbiome. Colonisation is driven by the ecology of the skin surface, which is highly variable depending on topographical location, endogenous host factors and exogenous environmental factors.
The cutaneous innate and adaptive immune responses can modulate the skin microbiota, but the microbiota also functions in educating the immune system8.
This relationship is modulated through signals from both the adaptive and innate immune systems and is under a constant barrage from endogenous and exogenous factors, such as environmental toxins, cosmetics, medications, allergens, pathogens, and injuries.9 These can cause a dysbiosis of the skin microbiome which is evidenced by Toll-like receptors (TLR) being released by our immune cells. These are an initial response mechanism of our immune system, to foreign invaders. (See our blog: Skin Microbiome).
The microbiome itself is additionally involved in detoxification processes and has been shown to be involved in metabolism of certain compounds. There is also potential for many of the inhabitants of the human microbiome to directly modulate host gene expression and modulate host detoxifying enzyme activity like cytochrome P450s (CYPs), dehydrogenases, and carboxylesterases.
Therefore, the skin microbiome may also influence skin’s ability to detoxify.10
Although the skin microbiome is specific and adaptive, it is intrinsically linked and influenced by the gut microbiome.
Skin conditions can be strongly affected by the gut flora and therefore digestive health is at the forefront of skin condition intervention. The gut modulates the skin via11:
- Systemic modulation of the immune system
- Modulation of inflammatory markers esp Th17, Th1 and NFk-B
- SCFA production support anti-inflammatory properties
- Metastasis of gut microbiota and their metabolites to the skin
Attenuation of gut flora with fibre, prebiotics, probiotics and fermented foods is important for maintaining a balanced gut and skin microbiome.
Nutritional products containing prebiotics and/or probiotics have a positive effect on skin by modulating the immune system and by providing therapeutic benefits for atopic diseases.12
Skin as an endocrine organ
The skin is exposed frequently to environmental stressors, which although may not be acutely toxic can have long term detriment to the skin and other organs of the body.
The skin has its own neuroendocrine system which regulates production of neuropeptides, neurohormones, neurotransmitters and hormones. This demonstrates that the skin has its own system designed to respond to stressors and there is support for healthy skin being important for stress resilience.13
The skin expresses multiple hormone receptors for peptide hormones, neurotransmitters and also steroid and thyroid hormones. The skin is highly influenced by thyroid function as well as reproductive and stress hormones, hormone dysfunctions should always be considered in skin conditions.
Additionally, many hormones are synthesised or activated in peripheral tissues, and the skin is one of the most significant sites for this13:
- A large proportion of androgens and oestrogens in men and women are synthesised locally in peripheral target tissue, such as the skin, from the inactive adrenal precursors DHEA and androstenedione.
- Insulin-like growth factor (IGF)-binding protein-3 message levels are greater in the skin than in the liver and circulating IGF-binding protein-3 concentrations are significantly increased by growth hormone and IGF-1, suggesting localised synthesis
- The skin also developed a fully functional peripheral HPA (hypothalamus-pituitary-adrenal) system where CRH (corticotrophin releasing hormone), ACTH (adrenocorticotropin hormone), and their receptors are produced in skin cells. Therefore, it is influenced by stress but also involved in modulating the stress response.
- The skin is the unique site of vitamin D (cholecalciferol synthesis) which derives from cholesterol.
It is important to note that there is again a two-way mutual relationship between hormones and the skin.
The skin is highly metabolically active, it is a large organ which has to regenerate itself every approximately every three weeks, and therefore it is logical that it is affected by trophic factors including thyroid, testosterone, oestrogen and insulin. These stimulate growth and regeneration of skin tissue. Likewise, the skin aids this activity by the inducement of peripheral synthesis and activation.
So, hormones also rely on the health and function of the skin for activity.
- As oestrogen declines, so does the rate at which the cells of the epidermis divide and reproduce14
- Stress impacts skins peripheral HPA15 and is associated with rosacea
- Skin is a target for thyroid hormones13 and dry skin is a symptom of underactive thyroid16
Therefore, in skin conditions, menopause, low testosterone, insulin resistance, thyroid and adrenal dysfunction should be considered.
Skin as an immune organ
The first line of defence against invading pathogens is the skin. This acts as a physical barrier, but also immune tissue, microbiome and detoxification enzymes make it an effective fortress against invaders. It actively protects from stress caused by injury, microbial treat, UV irradiation, and environmental toxins.9,17
Many of the skin’s immune capabilities are strongly influenced by the microbiome.
The skin also contains a complex network of a multitude of cell types, which maintain several vital processes such as inflammation and immune responses. It is thought it should be considered part of the lymphatic system as18:
- Keratinocytes create a unique microenvironment for the cells of the immune system by promoting immune recognition and cellular differentiation
- The dermis is represented by fibroblasts and endothelial cells followed by an array of immune cells which includes dendritic cells (DCs), macrophages, mast cells, NK-cells, neutrophils, basophils, eosinophils, αβ T lymphocytes, B-cells and platelets
- T lymphocytes exhibit tissue-specific tropism toward the epidermis and the lymphatic drainage system important for their function in immune regulation.
- Diversity in immune regulators makes the skin a unique organ to overcome pathogenic or foreign invasion
Supporting skin health and function as an organ system
When looking at skin health and disease, multiple factors can influence its function and integrity. Therefore, as with most conditions, interventions should be personalised depending on individual needs.
Factors that should be considered are:
- Support gut health– the gut is responsible for excretion of waste products therefore if it is dysfunctional this can affect excretion via the skin. Additionally, the gut and skin microflora are intrinsically linked and therefore gut flora should be supported. Consider: probiotic, fermented foods, high fibre, prebiotics12
- Support liver detoxification pathways to aid efficient removal of waste products. Include sulphur containing and brassica vegetables to support detoxification pathways such as garlic, onion, leeks, broccoli, kale, sprouts and cauliflower.
- Encourage sweating to support excretion pathways with saunas and exercise
- Consider the integrity of the skin when looking at hormone signalling, especially adrenal, reproductive, insulin and vitamin D signalling and/or dysfunction
- Support skin integrity with skin supporting nutrients including vitamins A, C, E and B5, zinc, selenium, and omega 3 fatty acids
- Avoid harsh soap, disinfectant etc on skin to maintain skin microbiome
- The skin is an organ of excretion, it has been shown that waste products including urea, lactic acids and ammonia as well as heavy metals are removed from the body via sweat glands. Encouraging sweating can be useful to support excretion pathways. Also ensuring other pathways of excretion (gut, liver and kidneys) are effective can be supportive for skin health.
- The skin possesses its own detoxification system and antioxidant systems which helps protect the skin form both environmental and endogenous toxins. If skin integrity is impaired, this can lead to build up of certain products in the skin.
- The skin has its own unique microbiome which plays an essential role in both immunity and detoxification. Supporting the gut microbiome is vital for the health of the skin microbiome. Which, if damaged can contribute to skin conditions.
- The skin is also essential for immune function as both a physical barrier and as a hub of immune activity. The skin’s health and integrity is fundamental to protection against foreign pathogens and also in the modulation of inflammation. Again, when this is compromised it is associated with other skin conditions and atopy (e.g., eczema)
- The skin also acts as an endocrine organ, it holds receptors for multiple hormones but is also the site for peripheral hormone synthesis or activation. Dysfunction of thyroid, HPA axis or reproductive hormone can affect skin quality and vice-versa.
Skin function references
- Baker LB. Physiology of sweat gland function: The roles of sweating and sweat composition in human health. Temperature: Multidisciplinary Biomedical Journal. 2019;6(3):211. doi:10.1080/23328940.2019.1632145
- Hoover E, Aslam S, Krishnamurthy K. Physiology, Sebaceous Glands. StatPearls. Published online October 14, 2021. Accessed October 12, 2022. https://www.ncbi.nlm.nih.gov/books/NBK499819/
- Sears ME, Kerr KJ, Bray RI. Arsenic, Cadmium, Lead, and Mercury in Sweat: A Systematic Review. J Environ Public Health. 2012;2012. doi:10.1155/2012/184745
- Hussain J, Cohen M. Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review. Evid Based Complement Alternat Med. 2018;2018. doi:10.1155/2018/1857413
- Auf Dem Keller U, Kümin A, Braun S, Werner S. Reactive Oxygen Species and Their Detoxification in Healing Skin Wounds. Journal of Investigative Dermatology Symposium Proceedings. 2006;11(1):106-111. doi:10.1038/SJ.JIDSYMP.5650001
- Liu XX, Sun C bin, Yang TT, et al. Decreased Skin-Mediated Detoxification Contributes to Oxidative Stress and Insulin Resistance. Exp Diabetes Res. 2012;2012. doi:10.1155/2012/128694
- Korkina L. Metabolic and redox barriers in the skin exposed to drugs and xenobiotics. Expert Opin Drug Metab Toxicol. 2016;12(4):377-388. doi:10.1517/17425255.2016.1149569
- Grice EA, Segre JA. The skin microbiome. Nat Rev Microbiol. 2011;9(4):244. doi:10.1038/NRMICRO2537
- Prescott SL, Larcombe DL, Logan AC, et al. The skin microbiome: impact of modern environments on skin ecology, barrier integrity, and systemic immune programming. World Allergy Organ J. 2017;10(1). doi:10.1186/S40413-017-0160-5
- Nichols RG, Peters JM, Patterson AD. Interplay Between the Host, the Human Microbiome, and Drug Metabolism. Hum Genomics. 2019;13(1):27. doi:10.1186/S40246-019-0211-9
- Ellis SR, Nguyen M, Vaughn AR, et al. The Skin and Gut Microbiome and Its Role in Common Dermatologic Conditions. Microorganisms. 2019;7(11):550. doi:10.3390/MICROORGANISMS7110550
- Al-Ghazzewi FH, Tester RF. Impact of prebiotics and probiotics on skin health. Benef Microbes. 2014;5(2):99-107. doi:10.3920/BM2013.0040
- Zouboulis CC. The skin as an endocrine organ. Dermatoendocrinol. 2009;1(5):250. doi:10.4161/DERM.1.5.9499
- Hall G, Phillips TJ. Estrogen and skin: the effects of estrogen, menopause, and hormone replacement therapy on the skin. J Am Acad Dermatol. 2005;53(4):555-568. doi:10.1016/J.JAAD.2004.08.039
- Chen Y, Lyga J. Brain-Skin Connection: Stress, Inflammation and Skin Aging. Inflamm Allergy Drug Targets. 2014;13(3):177. doi:10.2174/1871528113666140522104422
- Wilson SA, Stem LA, Bruehlman RD. Hypothyroidism: Diagnosis and Treatment. Am Fam Physician. 2021;103(10):605-613. Accessed October 13, 2022. https://pubmed.ncbi.nlm.nih.gov/33983002/
- Tsepkolenko A, Tsepkolenko V, Dash S, et al. The regenerative potential of skin and the immune system. Clin Cosmet Investig Dermatol. 2019;12:519-532. doi:10.2147/CCID.S196364
- Matejuk A. Skin Immunity. Arch Immunol Ther Exp (Warsz). 2018;66(1):45. doi:10.1007/S00005-017-0477-3
If you have questions regarding the topics that have been raised, or any other health matters, please do contact our team of Nutritional Therapists.
Last updated on 9th November 2022 by cytoffice