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A friend of mine, in a comment online, recently said:

Your body absorbs more minerals through your skin during a five minute shower than it does by drinking 64 oz (about 1.9 liter) of water over the span of a week.

That sounds like hogwash to me, but have there been any studies done regarding the absorption of minerals or chemicals (shampoos, soaps etc.) through your skin or by being inhaled when taking a shower?

Some sources of claims that the human body absorbs chemicals through the skin during showering:

  • minerals meaning what? – nico Jul 26 '11 at 21:07
  • 1
    @nico: The kind discussed here: who.int/water_sanitation_health/dwq/nutintakes.pdf – StriplingWarrior Jul 26 '11 at 21:43
  • Do you use the same water for drinking as for taking a shower? And how many and which minerals are in the water? In most cases, people use water from the area, they live in, and the amount of minerals might vary. – user unknown Jul 27 '11 at 1:52
  • +1 for being an interesting science question; however, see also How notable does a claim have to be for questions about it to be considered on-topic?. – ChrisW Jul 27 '11 at 3:03
  • I have attempted to make the claim notable by adding some (very unreliable!) sources of similar claims. Stripling, could you please edit the question to make it explicitly clear whether you mean to include chlorine (as opposed to chloride) in the question, and whether you mean to include inhaling while showering or strictly absorbing through the skin? – Oddthinking Jul 27 '11 at 6:02
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Shortly put: There are PLENTY of studies.

There are three uptake routes for chemicals while showering/bathing: Dermal, Inhalation and Ingestion.

When water is cleaned (chlorinated) you've got byproducts from the process. Some of the major byproducts are trihalomethanes (THMs), chloroform (CHCl3), bromodichlormethane (BDCM), dibromochloromethane (DBCM) and bromoform. Any/all of these can be present in the water after purification.

However, since I could go on about this all day, I'll limit my study sampling to just THMs and Chloroform studies.

THMs and showering/bathing:

There's been considerable research performed here:

Backer, LC, et al. (2000) Household exposures to drinking water disinfection byproducts whole blood trihalomethane levels. J. Expo Anal Environ Epidemol Jul-Aug;10(4):321-6.

The highest levels of THMs were found in the blood samples from people who took 10 min showers, whereas the lowest levels were found in the blood samples from people who drank 1 l of water in 10 min. The results from this study indicate that household activities such as bathing and showering are important routes for human exposure to THMs.

Miles, AM, et al. 2002. Comparison of trihalomethanes in tap water and blood. Environ Sci Technol Apr 15;36(8):1692-8.

Results indicated that THMs in the blood rose significantly as a result of showering, that showering shifted the THM distribution in the blood toward that found in the corresponding tap water, and that THMs measured in the blood of women living in the two locations reflected species and concentration differences in their respective tap waters. In general, blood concentrations were not significantly correlated with tap water concentrations. This finding suggests that other factors, in addition to tap water concentrations, may be important in determining THM concentrations in the blood

Nuckols, John R., et al. 2005. Influence of tap water quality and household water use activities on indoor air and internal dose levels of trihalomethanes. Environ Health perspect. July;113(7):863-870.

All hot water use activities yielded a 2-fold increase in blood or breath THM concentrations for at least one individual. The greatest observed increase in blood and exhaled breath THM concentration in any participant was due to showering (direct and indirect), bathing, and hand dishwashing. Average increase in blood THM concentration ranged from 57 to 358 pg/mL due to these activities. More research is needed to determine whether acute and frequent exposures to THM at these concentrations have public health implications. Further research is also needed in designing epidemiologic studies that minimize data collection burden yet maximize accuracy in classification of dermal and inhalation THM exposure during hot water use activities.

Lynberg, M., et al. 2001. Assessing exposure to disinfection by-products in women of reproductive age living in Corpus Christi Texas and Cobb county Georgia: descriptive results and methods. Environ Health Perspect. Jun;109(6):597-604.

We assessed exposure by sampling blood and water and obtaining information about water use habits and tap water characteristics. Two 10-mL whole blood samples were collected from each participant before and immediately after her shower. Levels of individual THM species (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) were measured in whole blood [parts per trillion (pptr)] and in water samples (parts per billion). In the Corpus Christi water samples, brominated compounds accounted for 71% of the total THM concentration by weight; in Cobb County, chloroform accounted for 88%. Significant differences in blood THM levels were observed between study locations. For example, the median baseline blood level of bromoform was 0.3 pptr and 3.5 pptr for participants in Cobb County and Corpus Christi, respectively (p = 0.0001). Differences were most striking in blood obtained after showering. For bromoform, the median blood levels were 0.5 pptr and 17 pptr for participants in Cobb County and Corpus Christi, respectively (p = 0.0001). These results suggest that blood levels of THM species vary substantially across populations, depending on both water quality characteristics and water use activities. Such variation has important implications for epidemiologic studies of the potential health effects of disinfection by-products.

THMs and Assessed Risk

Chowdhury, Shakhawat and Pascale Champagne. 2009. Risk from exposure to trihalomethanes during shower: Probabilistic assessment and control. Science of the Total Environment Feb 407(5):1570-1578.

Using THMs in warm water, cancer and non-cancer risks to human health were predicted for three major cities in Ontario (Canada). The parameters for risk assessments were characterized by statistical distributions. The total cancer risks from exposure to THMs during showering were predicted to be 7.6 × 10− 6, 6.3 × 10− 6 and 4.3 × 10− 6 for Ottawa, Hamilton and Toronto respectively. The cancer risks exceedance probabilities were estimated to be highest in Ottawa at different risk levels. The risks through inhalation exposure were found to be comparable (2.1 × 10− 6–3.7 × 10− 6) to those of the dermal contact (2.2 × 10− 6–3.9 × 10− 6) for the cities. This study predicted 36 cancer incidents from exposure to THMs during showering for these three cities, while Toronto contributed the highest number of possible cancer incidents (22), followed by Ottawa (10) and Hamilton (4). The sensitivity analyses showed that health risks could be controlled by varying shower stall volume and/or shower duration following the power law relationship.

Villaneuva, Christina M., et al. 2007. Disinfection by-products through ingestion, bathing, showering and swimming in pools. Am. J. Epidemiol. 165(2):148-156.

Lifetime personal information on water consumption and water-related habits was collected for 1,219 cases and 1,271 controls in a 1998–2001 case-control study in Spain and was linked with THM levels in geographic study areas. Long-term THM exposure was associated with a twofold bladder cancer risk, with an odds ratio of 2.10 (95% confidence interval: 1.09, 4.02) for average household THM levels of >49 versus ≤8 μg/liter. Compared with subjects not drinking chlorinated water, subjects with THM exposure of >35 μg/day through ingestion had an odds ratio of 1.35 (95% confidence interval: 0.92, 1.99). The odds ratio for duration of shower or bath weighted by residential THM level was 1.83 (95% confidence interval: 1.17, 2.87) for the highest compared with the lowest quartile. Swimming in pools was associated with an odds ratio of 1.57 (95% confidence interval: 1.18, 2.09). Bladder cancer risk was associated with long-term exposure to THMs in chlorinated water at levels regularly occurring in industrialized countries.

Chloroform

Weisel, C.P. and W.K. Jo 1996. Ingestion, inhalation and dermal exposures to chloroform and trichloroethane from tap water. Envron Health Perspect Jan;104(1):48-51.

Analysis of chloroform and trichloethene in expired breath, compounds regulated in water, was also used to determine uptake from tap water by each route (inhalation, ingestion, or absorption). Each route of exposure contributed to the total exposure of these compounds from daily water use. Further, the ingestion dose was completely metabolized before entering the bloodstream, whereas the dose from the other routes was dispersed throughout the body. Thus, differences in potential biologically effective doses depend on route, target organ, and whether the contaminant or metabolite is the biologically active agent.

Jo. Wan K., Weisel, Clifford P. and Paul J. Lioy. 1990. Routes of chloroform exposure and body burden from showering with chlorinated tap water. Risk Analysis Dec. 10(4):575-580.

The postexposure chloroform breath concentrations ranged from 6.0–21 μg/m3 for normal showers and 2.4 to 10 μg/m3 for inhalation-only exposure, while the pre-exposure concentrations were all less than the minimum detection limit of 0.86 μg/m3. According to an F-test, the difference between the normal shower and the inhalation-only exposures was considered significant at a probability of p= 0.0001. Based on the difference, the mean internal dose due to dermal exposure was found to be approximately equal to that due to the inhalation exposure. The effect of the showering activities on the concentration of chloroform shower air was examined by comparing air concentrations during a normal shower with the air concentrations obtained when the shower was unoccupied. The F-test showed that there is no significant difference between the two sets of data

Chloroform and Cancer Risk (Good news here!)

Lévesque, B. et, al. 2002. Cancer risk associated with household exposure to chloroform. J. Toxicol Environ Health A Apr 12;65(7):489-502.

Exposure to CHCl3 was assessed for 18 men (age: mean 38 years; range 23-51) following a 10-min shower in their respective residences located in the Quebec City region (Canada). CHCl3 concentration was measured in alveolar air samples collected before, immediately after, and 15 min and 30 min following the shower. Indoor air and water concentrations were determined concomitantly. Mean CHCl3 concentrations in the air of the shower stall and in water were respectively 147 microg/m3 (SD = 56.2 microg/m3) and 20.1 microg/L (SD = 9.0 microg/L). Water concentrations were comparable to those documented in a large proportion of distribution networks in Canada. The mean increase in alveolar air CHCl3 concentration (deltaCHCIALV) at the end of the shower was 33 microg/m3 (SD = 14.7 microg/m3). A multiple-regression analysis revealed that deltaCHCl3ALV values were only associated with chloroform concentration in air of the shower stall. DeltaCHCl3ALV were described using a physiologically based pharmacokinetic (PBPK) model. This model was then used to estimate concentrations of CHCl3 metabolites bound to liver and kidney macromolecules following a shower, and also according to exposure scenarios that integrate drinking-water ingestion and air inhalation. The concentration predicted in the liver following a worst-case exposure scenario was 0.41 microg CHCl3 equivalents/kg of tissue, some 6,000 times lower than the lowest concentration that did not increase the incidence of hepatic tumors in laboratory animals. Data indicate that for this range of exposure the safety margin appears therefore considerable with respect to the potential carcinogenic effect of household exposure to CHCl3.

  • But what is our rate of excretion for the 2. If the levels drop back to normal with in 15 -30 minutes of the shower but maintain for the consumption of water then drinking would still seem like a far more effective delivery. – Chad Aug 10 '11 at 13:53
  • @Chad From the Weisel & Jo report "the ingestion dose was completely metabolized (aka broken down into other chemical compounds - my definition) before entering the bloodstream, whereas the dose from the other routes was dispersed throughout the body." Blood sampling occurred (in most studies) after a half hour period - therefore levels were not 'dropped back to normal'. – Darwy Aug 10 '11 at 14:23
  • This is very interesting as I grew up in a town whose water was contaminated by 50's waste that we did not drink but we used it for showers/pools/etc. I wonder how much of that contributed to the relitively rare diseases that seem to be more common there. – Chad Aug 10 '11 at 15:17
  • That'd depend on the chemical found in the water, the number of baths/showers/pool usage occurrences as well as the individual. Without any data, I won't try to make a prediction. Is it possible it contributed? Sure. Is it a certain contributor? I can't answer that. – Darwy Aug 10 '11 at 15:43
  • The studies that compare showering and bathing pretty much prove that chemicals are not absorbed dermally (through the skin), but inhaled. No surprise, any engineer will tell you that the fastest way to vaporize a hot liquid is by breaking it up in droplets. – MSalters Oct 18 '11 at 8:53

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