In the Yoga Mala, Sri K. Pattabhi Jois highlights Surya Namaskara as not only a destroyer of physical impurities, but also mental and karmic baggage (p.51). One popular theory suggests heat to be a catalyst for purging toxins in sweat, which in turn removes subtle barriers that would otherwise prevent the cultivation of health and wellbeing. However, in recent years this line of argument has become the subject of much scrutiny in the lay press. For example, a recent article published by the Huffington Post titled, “5 Yoga Myths Even Devoted Yogis Still Believe” lists the excretion of toxins in sweat as ‘Myth 1’ (Wise). Over the past week, I’ve been reviewing scientific literature in order better understand the true connection between heat, perspiration, xenobiotics (i.e. toxins) and health. Along the way, I’ve discovered that the benefits of sweating are more so linked to the secretion and reabsorption of therapeutic biomolecules than many yoga critics realize.
One observation backed by both personal observation and academic research is that the composition of sweat is highly complex and uniquely reflects the individual. Although Huffington Post author Abigail Wise may be correct by asserting “When you sweat, you release water, salt and electrolytes, not toxins,” her statement on the composition of sweat is most certainly an abstraction. For over 100 years scientists have know that sweat also contains free amino acids, and we only now starting to understand their significance. For example, a particularly prevalent residue named serine confers protection towards irritants. One theory suggests that the enrichment of endogenous serine containing membrane sphingolipids is an important factor for preventing skin pathologies (Kutyshenko et al). Simply put, serine may play an unseen role in nourishing our skin from the inside out.
The science of sweat also reveals interesting patterns in skin differentiability based on location. Some of the very first research aimed at elucidating these patterns were conducted by two biologists named Ruth Van Heyningen and J. S. Weiner. Between 1949 and 1951 these researchers measured the chloride, lactate, and urea composition in both the arm and back sweat of healthy male subjects. Their results show that arm perspiration contains about about 2.5 times higher concentration of each of the three trace components compared to body sweat (Heyningen et al). Modern research inspired by these landmark finding has shown that sweat from one’s face contains enhanced glycerol content compared to one’s back and arm sweat. The mechanism for these finding most likely reflects the presence of sebaceous glands secretions containing free fatty acids, which are readily converted to glycerol by benign skin flora (Kutyshenko et al). In this way, both and the integrity of one’s arm skin and the suppleness of one’s face are enhanced through regular sweaty exercise.
The modern technique of NMR spectroscopy has offered scientists a glimpse into the previously unknown composition of sweat. Although NMR can neither confirm nor deny the identity of non-bonded transition elements (e.g. metal ions), the presence of many polyatomic ions can be deduced in perspiration (Razmiafshari et al). One tiny cation which is thought to play a rather important role in our innate immune system is ammonium (NH4+). When ammonium is secreted and reabsorbed within our skin’s epidermis, an added defensive layer in created preventing most bacteria from growing there (Kutyshenko et al). According to one theory, bacteria which ingest ammonium will be exposed to its antimicrobial conjugate base ammonia, and therefore those who sweat regularly will likely have higher levels of ammonium in their cells limiting exposure to harmful bacteria. When our skin is no longer hospitable to gas producing bacteria the amino acids and sugars found in sweat cannot be used as their fuel source. In this way, sweating out ammonium can also lessen one’s xenobiotic load by promoting a strong innate immune system.
Lessening one’s xenobiotic load is one of the most widely discussed themes of holistic medicine. Based on my brief investigation, I currently find there to be better scientific evidence supporting the conclusion that sweat is a medium which promotes skin health, rather than detoxification. Remarkably, it would seem that scientific thought is beginning to complement the traditional teachings of yoga gurus. In the 15th century, Swami Swatmarama advocated rubbing sweat back into one’s skin after practice. In his words, “As a result there occurs firmness and lightness of the body” (Hatha Yoga Pradipika ii : 13). This technique is still taught guru to disciple in many active yoga lineages. On perspiration, Jois writes, “The practitioner will grow weaker and weaker over time…by exposing it to the air or by drying it with a towel or cloth.” Although these claims may be difficult for westerners to truly accept, I can personally attest to a tangential claim, that perspiration starts to lose its noxious odor after about one week of consistent practice. As a result, the act of rubbing my own sweaty body with outstretched fingers begins to feel paradoxically hygienic. I personally hope future scientists will help us yogis deduce the reason why our sweat seems to become progressively cleaner with practice.
Sri K Patthabhi Jois. Yoga Mala. Patanjali Yoga Shala. New York, NY. 1999.
Abigail Wise. 5 Yoga Myths Even Devoted Yogis Still Believe. The Huffington Post. 2014.
Kutyshenko VP, Molchanov M, Beskaravayny P, Uversky VN, and Timchenko MA. Analyzing and Mapping Sweat Metabolomics by High-Resolution NMR Spectroscopy. PLoS One, 2011; 6(12):e28824
Van Heyningen R, and Weiner JS. A Comparison of Arm Bag Sweat and Body Sweat. J Physiol, 1952; 116:395-406.
Razmiafshari M, Kao J, d’Avignon A, and Zawia NH. NMR identification of heavy metal-binding sites in a synthetic zinc finger peptide: toxicological implications for the interactions of xenobiotic metals with zinc finger proteins. Toxicol Appl Pharmacol, 2001; 172(1):1-10.