Swimming offers a myriad of benefits for both physical and mental well-being.1 It is reported as the fourth most popular sport in the U.S., and it has been estimated that 4.7 million adults worldwide swim at least twice a month.46 However, it can cause dry, itchy skin and atopic dermatitis due to barrier disruption.2 Chronic exposure of chlorine and its lesser known byproducts in swimming pools is not widely studied and its negative impact on the skin barrier and hair is not generally discussed, underscoring the need for further research and awareness in this area – with an opportunity to formulate new products that address the chronic effects of chlorine and its byproducts in skin and hair. This article reviews the chemistry of swimming pool water as well as the (limited) research in the literature about the effects of chronic exposure to swimming pool water in skin and hair. It also offers ideas for product development to address these effects.
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Swimming offers a myriad of benefits for both physical and mental well-being.1 It is reported as the fourth most popular sport in the U.S., and it has been estimated that 4.7 million adults worldwide swim at least twice a month.46 However, it can cause dry, itchy skin and atopic dermatitis due to barrier disruption.2 Chronic exposure of chlorine and its lesser known byproducts in swimming pools is not widely studied and its negative impact on the skin barrier and hair is not generally discussed, underscoring the need for further research and awareness in this area – with an opportunity to formulate new products that address the chronic effects of chlorine and its byproducts in skin and hair. This article reviews the chemistry of swimming pool water as well as the (limited) research in the literature about the effects of chronic exposure to swimming pool water in skin and hair. It also offers ideas for product development to address these effects.
Swimming Pool Water: Chemical Composition
In order to understand the effects of swimming pool water in skin and hair, it is important to understand the composition of pool water. Maintaining the optimal alkalinity level is vital for ensuring the well-being of swimmers, therefore a pH balance of pool water within the safe range of 7.2 to 7.6 is maintained using sodium bicarbonate, sodium bisulfate or muriatic acid. To ensure a safe swimming environment, disinfectants such as chlorine or bromine are typically added to swimming pools. These chemicals work to eliminate bacteria, viruses and other microorganisms that would otherwise thrive in this environment.
However, when chlorine reacts with water, it creates hypochlorous acid, which may react with other substances in the water, forming disinfection by-products (DBP). DBPs are ineffective sanitizers and may possibly lead to skin and eye irritation and an unpleasant odor in swimming pools.3 One recent study identified more than 100 DBPs in pool water, as measured by gas chromatography/mass spectrometry (GC/MS), photometry and ion chromatography. Many of the DBPs were new and had not been previously reported.4
In addition, nitrogen-containing DBPs were present, most likely formed from human inputs such as urine, sweat and skin cells.5, 6 Table 1 lists some of the DBPs found in chlorinated and brominated pools.4 The highest levels of DBPs detected were chloroform and bromoform, both highly toxic substances. While brominated pools contained a low level of chloroform (0.1 μg/L), chlorinated pools contained relatively higher levels of bromoform (7.2 μg/L), presumably from the presence of bromide in untreated water before chlorination, which then reacts with chlorine that is added during chlorination.
The impact of chlorine and DBPs on skin can be divided in three major areas: 1) skin/dermal penetration, 2) skin microbiome and acne, and 3) the skin barrier.
(click to enlarge) Table 1: Free chlorine, chloramine and THM levels in tested pool water; see Ref 4.
1. Effect of DBPs on Skin/Dermal Penetration
Xu conducted a study40 investigating the permeation through human skin of DBPs such as trihalomethanes (THMs), haloketones (HKs) and haloacetic acids (HAA) in chlorinated water. Using in vitro diffusion chambers, THMs were found to be approximately 10 times more permeable than HKs. These haloketones and THMs could cause oxidative stress on different layers in skin, although longer term studies and their impact on skin and skin permeation are unknown.
Erdinger, et al.,7 studied various pathways of THM uptake in swimming pools – dermal, by inhalation or by swallowing. In 17 participants, the researchers quantified the body burden resulting from exposure to three different concentrations of chloroform in water and air of an indoor swimming pool during a 60-min exercising period. Chloroform concentrations were measured in blood samples before and after each exercise period. The blood chloroform concentration of participants with scuba tanks was 0.32 + 0.26 μg/L; without scuba tanks was 0.99 + 0.47 μg/L; and for individuals walking around the pool, its was 0.31+ 0.25 μg/L. These results indicated the majority of THMs are taken up via the respiratory pathway while a significant amount is also taken up by the skin.7 In a separate study of competitive swimmers, dermal uptake accounted for up to 80% of THM blood levels.8
A study in cancer patients conducted in hospitals in Spain from 1998 to 2001 revealed a heightened risk of bladder cancer among those who reported ever being in a pool.9-12 This elevated risk may be linked to trihalomethanes, which have shown a positive association with bladder cancer.10 These findings are concerning and display the importance of taking preventative measures to reduce the uptake of DBPs through skin.
2. Effects of Pool Water on Skin Microbiome and Acne
Exposure to chlorine leaves skin dry, leading to itchiness and discomfort driven by an interplay of complex mechanisms. Firstly, exposure to higher pH pool water increases skin’s native physiologically balanced pH of around 4.7.13 This increased pH could lead to a decrease in stratum corneum cohesion,2 which may lead to microbiome dysbiosis.14 Furthermore, an increase in skin pH is also known to change the skin's permeability and to strip away essential lipids such as sebum,15 causing dry, itchy and inflamed skin.16 Indeed, one small study in nine women found that recreational swimming in pool water significantly decreased sebum levels on the skin.17
A healthy sebum composition also plays a critical role in maintaining lipid balance and the skin barrier, and protecting against infections. In fact, Nakatasuji conducted a study where lauric acid, a free fatty acid (FFA) in sebum, was tested against the skin bacteria Propionibacterium acnes, Staphylococcus aureus and Staphylococcus epidermidis. The results showed it took 15× less lauric acid to inhibit their growth than the amount of benzoyl peroxide needed for the same effect.18
In other words, lauric acid, which is present in healthy sebum, was significantly more effective than benzoyl peroxide at preventing the growth of these bacteria.18 This demonstrates sebum's crucial role in protecting our skin. In addition, lauric, palmitic and oleic acids, which are common free fatty acids found in human sebum, have been found to boost the production of antimicrobial peptides and increase the antimicrobial activity of human skin cells against the bacteria P. acnes. This suggests that the free fatty acids in sebum help to disinfect the skin, which enhances the skin’s immune defense.19
What’s more, although chlorine may act as a mild disinfectant to acne-causing bacteria, the drying, sebum-stripping effects, moisture loss, and melting and dilution of the sebum16 may actually lead to the overproduction of oil by the skin in an attempt to compensate – contrarily clogging pores and contributing to acne breakouts.15
Interestingly, in a study of 24 swimmers, fluorescence photography revealed how bacteria such as C. acnes and Pseudomonadaceae contribute to acne in adolescent swimmers; after swimming, levels of Pseudomonadaceae increased while those of C. acnes remained the same.20 This suggests that repeated exposure to chlorine might affect the balance of bacteria on the skin and possibly lead to the development of acne in swimmers.
3. Effects of Pool Water on Skin Barrier
Exposure to pool water can also increase transepidermal water loss (TEWL), indicating a compromised stratum corneum.21 One study of 58 athletes, including elite swimmers and football players, measured TEWL before, immediately after and 30 min after 2-hr training sessions. Among swimmers, the median TEWL levels increased from baseline values of 8.5 g/m²/hr to 14.3 g/m²/hr immediately after training and remained elevated at 13.2 g/m²/hr 30 min post-training. Although football players experienced a noticeable increase in TEWL from 8.1 g/m²/hr to 10.6 g/m²/hr immediately after training, which slightly decreased to 9.7 g/m²/hr 30 min post-training, the change in TEWL for swimmers was much more significant.2 These findings suggest that swimming, likely due to exposure to chlorine and other chemicals in pools, can damage the skin's stratum corneum, leading to increased water loss and potentially compromised skin barrier function.
Eczema, a condition that affects more than 31 million Americans,22 is a skin condition that leads to itchiness, dry skin, rashes and even skin infections. Atopic dermatitis (AD), the most common type of eczema, is usually caused by an overactive immune system and it, too, causes dry and itchy skin. Exposure to soaps and fabric softeners are common causes for flare-ups but exposure to chlorine can also cause them; in fact, eczema has been shown to be more common in swimmers than individuals in other sports.23-25
One study in AD patients investigating the impact of residual chlorine in bathing water on the functionality of the skin’s outermost layer, the stratum corneum (SC), showed significantly reduced skin hydration when they were exposed to water with as little as 1.0 mg/L chlorine. Their skin’s water-holding capacity was notably less even at lower chlorine levels, compared with normal control subjects. This suggests that chlorine exposure may contribute to the development or worsening of AD symptoms in affected individuals.26 In fact, it has been shown that prolonged contact with chloroform can result in dermatitis.27
4. Effects of Pool Water in Hair
In hair, chlorine most commonly causes split ends for four reasons: the stripping of natural oils, the weakening of hair structure, oxidative stress and increased porosity. The stiff and crunchy feeling of hair after one exits a pool is due to the chlorine binding to hair keratin,28 stripping away natural oils, which leaves it dry and brittle. These oils are essential for maintaining the moisture balance of hair, and when the moisture content is low, hair is more prone to damage such as split ends. In addition, oxidative stress caused by chlorine can break down hair's outer protective layer, the cuticle,29 which additionally increases the chance of split ends. The friction of the water against hair can even damage the cuticle, as one study of the Japanese National Swimming team using electron microscopy showed; this also led to the discoloration of hair.29
Chlorine oxidation is another way hair becomes discolored.30 During oxidation, the chlorine can react with metals such as copper to form a sticky copper-chlorine complex that attaches to the hair shaft, turning brown hair a lighter color, or lighter-colored/blond hair a greenish color.31
Discussion: Opportunities for New Product Innovation
This review highlights current gaps in terms of treatments for or protection against the negative effects in skin and hair caused by exposure to chlorinated and brominated DBPs. Based on the evidence, three product innovation opportunities emerge.
- Reducing the interaction and permeation of DBPs on skin. While the long-term effects of DBPs are not fully known, they may induce oxidative stress in skin; furthermore, their dermal penetration can lead to systemic exposure. A strategy to reduce the dermal uptake and permeation of DBPs may be beneficial for skin health. For example, one can hypothesize that, since sunscreens or compositions with skin-friendly polymeric film formers can form a physical barrier, they may be used to minimize direct contact between DBPs and skin. Although several swim products such as moisturizers are currently offered in the market, these treat the symptoms rather than preventing the cause: exposure to hundreds of DBPs. The ideal product would entail creating a water-resistant barrier cream that protects skin against exposure to, and the permeation of, DBPs.
- Maintaining skin pH, microbiome. Another strategy would be to create products that help maintain the pH of skin and/or restore the skin microbiome. This would entail using ingredients that restore the pH balance of skin as well as skin-friendly prebiotics or postbiotics.
- Alternative means of pool water disinfection. Beyond the skin itself, alternate strategies to disinfect pools may be considered. The use of plant-based extracts like Moringa oleifera, for example, is being investigated.32
The past two decades have experienced increased interest in swimming, thanks in part to the publicity around it – especially with the Olympics – and the known health benefits it provides.47 As more individuals turn to swimming for heath and recreation, this presents a market opportunity for product developers; it also warrants further investigation into how chronic exposure to chlorine and its lesser-known byproducts in swimming pools affect skin and hair.
References
1. Lee, B.A. and Oh, D.J. (2015, Oct 30). Effect of regular swimming exercise on the physical composition, strength, and blood lipid of middle-aged women. J Exerc Rehabil, 11(5) 266-71; doi: 10.12965/jer.150242; PMID: 26535217; PMCID: PMC4625655.
2. Paciência, I., Rodolfo ... Moreira, A., et al. (2021, Jan 14). Effects of exercise on the skin epithelial barrier of young elite athletes-swimming comparatively to non-water sports training session. Int J Environ Res Public Health, 18(2) 653; doi: 10.3390/ijerph18020653; PMID: 33466624; PMCID: PMC7828688.
3. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. (2004). Some drinking-water disinfectants and contaminants, including arsenic. Lyon (FR): International Agency for Research on Cancer. (IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 84.); Chloramine, available at https://www.ncbi.nlm.nih.gov/books/NBK402265/
4. Richardson, S.D., DeMarini, D.M., ... Villanueva, C.M., et al. (2010 Nov). What's in the pool? A comprehensive identification of disinfection by-products and assessment of mutagenicity of chlorinated and brominated swimming pool water. Environ Health Perspect, 118(11) 1523-30, doi: 10.1289/ehp.1001965; PMID: 20833605; PMCID: PMC2974688.
5. Kim, H., Shim, J. and Lee, S. (2002). Formation of disinfection by-products in chlorinated swimming pool water. Chemosphere, 46 123-130.
6. LaKind, J.S., Richardson, S.D. and Blount, B.C. (2010). The good, the bad and the volatile: Can we have both healthy pools and healthy people? Environ Sci Technol, 44 3205 - 3210.
7. Erdinger, L., Kuhn, K.P., ... Nohynek, B., et al. (2004). Pathways of trihalomethane uptake in swimming pools. Int J Hyg Environ Health, 207 571 - 575.
8. Lindstrom, A.B., Pleil, J.D. and Berkoff, D.C. (1997 Jun). Alveolar breath sampling and analysis to assess trihalomethane exposures during competitive swimming training. Environ Health Perspect, 105(6) 636-42; doi: 10.1289/ehp.97105636; PMID: 9288498; PMCID: PMC1470079.
9. Cantor, K.P., Hoover, R., ... Altman, R., et al. (1987). Bladder cancer, drinking water source and tap water consumption: A case-control study. J Natl Cancer Inst, 79(6) 1269 - 1279.
10. Cantor, K.P., Villanueva, C.M., ... Garcia-Closas, M., et al. (2010). Polymorphism GSTT1, GSTZ1 and CYP2E1, disinfection by-products and risk of bladder cancer in Spain. Environ Health Perspect, 118 1545 - 1550.
11. McGeehin, M.A., Reif, J.S., Becherm, J.C. and Mangione, E.J. (1993). Case-control study of bladder cancer and water disinfection methods in Colorado. Am J Epidemiol, 138(7) 492 - 501.
12. Villanueva, C.M., Cantor, K.P., ... Tardon, A., et al. (2007). Bladder cancer and exposure to water disinfection by-products through ingestion, bathing showering and swimming in pools. Environ Res, 165(2) 148 - 156.
13. Lambers, H., Piessens, S., Bloem, A., Pronk, H. and Finkel, P. (2006, Oct). Natural skin surface pH is on average below 5, which is beneficial for its resident flora. Int J Cosmet Sci, 28(5) 359-70;doi: 10.1111/j.1467-2494.2006.00344.x. PMID: 18489300.
14. Aveeno. (Accessed 2024, Oct 25). Healthy microbiome, health skin. Available at https://hcp.aveeno.ca/hcp/microbiome
15. Makrantonaki, E., Ganceviciene, R. and Zouboulis, C. (2011, Jan). An update on the role of the sebaceous gland in the pathogenesis of acne. Dermatoendocrinol, 3(1) 41 - 9; doi: 10.4161/derm.3.1.13900; PMID: 21519409; PMCID: PMC3051853.
16. Freiman, A., Barankin, B. and Elpern, D.J. (2004, Nov 23). Sports dermatology part 2: Swimming and other aquatic sports. CMAJ, 171(11) 1339 - 41; doi: 10.1503/cmaj.1040892. PMID: 15557582; PMCID: PMC527331.
17. Gardinier, S., Guéhenneux, S., Latreille, J., Guinot, C. and Tschachler, E. (2009 Nov). Variations of skin biophysical properties after recreational swimming. Skin Res Technol, 15(4) 427 - 32; doi: 10.1111/j.1600-0846.2009.00382.x. PMID: 19832953.
18. Nakatsuji, T., Kao, M.C., ... Fang, J.Y., et al. (2009). Antimicrobial property of lauric acid against Propionibacterium acnes: Its therapeutic potential for inflammatory acne vulgaris. J Invest Dermatol, 129 2480 - 2488.
19. Nakatsuji, T., Kao, M.C., Zhang, L., Zouboulis, C.C., Gallo, R.L. and Huang, C.M. (2010, Apr). Sebum free fatty acids enhance the innate immune defense of human sebocytes by upregulating beta-defensin-2 expression. J Invest Dermatol, 130(4) 985-94; doi: 10.1038/jid.2009.384; Epub 2009 Dec 24; PMID: 20032992; PMCID: PMC3057125.
20. Morss-Walton, P.C., McGee, J.S., Rosales Santillan, M., ... Kimball, A.B., et al. (2022, Geb 17). Yin and yang of skin microbiota in "swimmer acne." Exp Dermatol, 31(6) 899 - 905; doi: 10.1111/exd.14535; Epub 2022 Feb 17; PMID: 35118730.
21. Green, M., Kashetsky, N., Feschuk, A. and Maibach, H.I. (2022, Feb 25). Transepidermal water loss (TEWL): Environment and pollution-A systematic review. Skin Health Dis, 2(2):e104; doi: 10.1002/ski2.104; PMID: 35677917; PMCID: PMC9168018.
22. National Eczema Association. (Accessed 2024, Oct 25). What is eczema? Available at nationaleczema.org/eczema/
23. Lazarov, A., Nevo, K., Pardo, A. and Froom, P. (2005). Self-reported skin disease in hydrotherapists working in swimming pools. Contact Dermat, 53 327 - 331; doi: 10.1111/j.0105-1873.2005.00699.x.
24. Basler, R.S.W., Basler, G.C., Palmer, A.H. and Garcia, M.A. (2000). Special skin symptoms seen in swimmers. J Am Acad Dermatol, 43 299 - 305; doi: 10.1067/mjd.2000.107495.
25. Font-Ribera, L., Kogevinas, M., Zock, J.P., Nieuwenhuijsen, M.J., Heederik, D. and Villanueva, C.M. (2009). Swimming pool attendance and risk of asthma and allergic symptoms in children. Eur Respir J, 34 1304 - 1310. doi: 10.1183/09031936.00180608
26. Seki, T., Morimatsu, S., Nagahori, H. and Morohashi, M. (2003 Mar). Free residual chlorine in bathing water reduces the water-holding capacity of the stratum corneum in atopic skin. J Dermatol, 30(3) 196-202; doi: 10.1111/j.1346-8138.2003.tb00371.x. PMID: 12692355.
27. Bingham B., Cohrssen, B. and Powell, C. (eds) (2001, Sep). Patty's Toxicology, 5th edition in 9 volumes. Available at https://pubs.acs.org/doi/10.1016/S1074-9098%2801%2900241-6
28. Schmidt, C. (2021, Feb 26). What does chlorine do to your hair? Formulate. Available at https://www.formulate.co/journal/p/what-does-chlorine-do-to-your-hair
29. Nanko, H., Mutoh, Y., ... Mizoguchi, M., et al. (2000 Oct). Hair-discoloration of Japanese elite swimmers. J Dermatol, 27(10) 625-34; doi: 10.1111/j.1346-8138.2000.tb02243.x. PMID: 11092265.
30. Pires-Oliveira, R. (2010). Hair color damage caused by exposure to chlorinated water in the presence of ultraviolet radiation. Available at https://www.researchgate.net/publication/236109930_Hair_color_damages_caused_by_exposure_to_chlorinated_water_in_the_presence_of_ultraviolet_radiation
31. Mascaró, J.M., Jr., Ferrando, J., Fontarnau, R., Torras, H., Domínguez, A. and Mascaró, J.M. (1995, Jul). Green hair. Cutis, 56(1) 37-40; PMID: 7555100.
32. Brinin-Yauri, U.A. (2012, Jan). The use of some plants in water purification. Research Gate. Available at https://www.researchgate.net/publication/264943062_The_use_of_some_plants_in_water_purification
33. Richardson, S.D. (1998). Drinking water disinfection by-products. In: Meyers, R.A., ed., The encyclopedia of environmental analysis and remediation, vol. 3, New York, Wiley, pp 1398 - 1421.
34. Richardson, S.D., Plewa, M.J., Wagner, E.D., Schoeny, R. and DeMarini, D.M. (2007). Occurrence, genotoxicity and carcinogenicity of regulated and emerging disinfection by-products in drinking water: A review and roadmap for research. Mutat Res, 636 178 - 242.
35. Xu, W. and Weisel, C.P. (2004). Human respiratory uptake of chloroform and haloketones during showering. J Exp Anal Environ Epidemiol, 15 6 - 16.
36. Xu, X. and Weisel, C.P. (2005). Dermal uptake of chloroform and haloketones during bathing. J Exp Anal Environ Epidemio, 15 289 - 296.
37. Rivera-Núñez, Z., Wright, J.M., ... Savitz, D.A., et al. (2012, May). Comparison of trihalomethanes in tap water and blood: A case study in the United States. Environ Health Perspect, 120(5) 661 - 7; doi: 10.1289/ehp.1104347; Epub 2012 Jan 26. PMID: 22281753; PMCID: PMC3346785.
38. McCarthy, C. (2023, May 15). Swimming and skin: What to know if a child has eczema. Harvard Health. Available at www.health.harvard.edu/blog/swimming-and-skin-what-to-know-if-a-child-has-eczema-202305152935.
39. Li, Jiang-Hua, et al. (2015, Mar 5). Health effects from swimming training in chlorinated pools and the corresponding metabolic stress pathways. PLOS ONE. Available at https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0119241
40. Xu, X., Mariano, T.M., Laskin, J.D. and Weisel, C.P. (2002, Oct 1). Percutaneous absorption of trihalomethanes, haloacetic acids and haloketones. Toxicol Appl Pharmacol, 184(1) 19 - 26; PMID: 12392965.
41. Perkin, M.R., Craven, J., ... Flohr, C., et al. (2016, Aug). Enquiring about tolerance study team. Association between domestic water hardness, chlorine and atopic dermatitis risk in early life: A population-based cross-sectional study. J Allergy Clin Immunol, 138(2) 509 - 16; doi: 10.1016/j.jaci.2016.03.031; Epub 2016 Apr 28; PMID: 27241890.
42. Li, J.H., Wang, Z.H., ... Lin, Y.J., et al. (2015, Mar 5). Health effects from swimming training in chlorinated pools and the corresponding metabolic stress pathways. PLoS One, 10(3):e0119241; doi: 10.1371/journal.pone.0119241; PMID: 25742134; PMCID: PMC4351252.
43. Fernández-Luna, Á., Burillo, P., Felipe, J.L., del Corral, J., García-Unanue, J. and Gallardo, L. (2016). Perceived health problems in swimmers according to the chemical treatment of water in swimming pools. Eur J Sport Sci, 16(2) 256 - 65; doi: 10.1080/17461391.2014.1001877; Epub 2015 Jan 21; PMID: 25604467.
44. Sivaranjani, S. and Rakshit, A. (2016, Mar). Indigenous materials for improving water quality. Available at https://www.researchgate.net/publication/305531026_Indigenous_materials_for_improving_water_quality
45. IPCS INCHEM. (Accessed 2024, Oct 25). Chloroform. Available at https://www.inchem.org/documents/pims/chemical/pim121.htm
46. PlayToday. (2024, Mar 7). 17 Swimming statistics to know in 2024. Available at https://tinyurl.com/275wmrzx
47. FHC Sports Report. (2024, Apr 23). How much has the sport of swimming changed? Available at https://fhcsportsreport.com/31686/showcase/how-much-has-the-sport-of-swimming-changed/
