chlorine-shower-water-skin
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Chlorine shower water skin questions usually ask two things: does the chlorine in tap water get through the skin, and does that harm the skin. The 2011 study used here answers part of the first question, for a different group of by-products called haloacetonitriles and for chloral hydrate. It used pieces of human skin in a laboratory. It did not measure skin damage, dryness or irritation, and it did not test chlorine itself. This guide explains what the study measured and where its findings stop.
Quick answer
- The study measured how fast the by-products passed through cadaver skin. For the haloacetonitriles the permeability coefficient (Kp) was 0.099 to 0.167 cm/hr. For chloral hydrate it was 0.0039 cm/hr.
- In the authors’ simulation of an average US population, the dermal dose of haloacetonitriles was 0.39 to 0.75 times their drinking-water ingestion dose. For chloral hydrate it was about 0.02 times.
- The authors write that dermal exposure to these compounds “seems to be a significant route of exposure” during bathing and swimming.
- The sources do not say that chlorine, or these by-products, damage skin or hair. They do not measure any skin condition at all.
What the 2011 study measured
The study by Trabaris, Laskin and Weisel was published in the Journal of Applied Toxicology in 2011. Its stated aim was to measure the “permeation coefficients (Kp) for haloacetonitriles (HANs) and chloral hydrate (CH)”, which the abstract describes as important cytotoxic DBPs. DBP is short for disinfection by-product. The authors explain that these by-products are “formed by reactions of disinfectants such as chlorine with humic substances and other organic material commonly found in water”.
A Kp is a measure of how quickly a compound crosses a layer of tissue under set conditions. It is a laboratory number. It is not a count of how much reaches the blood during a shower. The study used “human cadaver skin sections from the torso”, and the skin was “dermatomed to a thickness between 0.25 and 0.28 mm”. Dermatomed means the skin was cut to a set thickness. For the main measurements the dermis was removed, because the authors state that “the dermis was removed when skin tissue was used for in vitro permeation studies”.
The authors describe the conditions in the lab. The Kp values were “measured using fully hydrated dermatomed torso skin at 37 °C”. The skin was frozen before use, and the authors explain that “Human cadaver skin was frozen prior to use, so no metabolic activity was expected”. They also state that “It was assumed that any solutes that passed through the skin did so by passive diffusion”. Passive diffusion means the compound moves across the skin without the skin’s cells actively carrying it. The authors do not claim that the living skin of a person works the same way.
Before each skin sample was used, the authors tested it. They measured the passage of tritiated water. Skin was rejected if the Kp for water was “greater than 2.5 × 10 −3 cm/hr” or if more than 0.29 percent of the tracer passed through after a 20-minute exposure. This test checks that the sample is intact. It does not show anything about the skin of a person who showers.
The numbers, in one table
The table below uses only the values the paper states. Where the paper gives a single value, the table shows it. Where it gives a range, the table shows the range.
| Compound group | Measured Kp (cm/hr) | Modelled dermal dose as a share of ingestion dose, average population | Modelled ratio, chlorinated pool use |
|---|---|---|---|
| Haloacetonitriles (HANs) | 0.099 to 0.167 | 0.39 to 0.75 times | 0.304 to 2.25 times |
| Chloral hydrate (CH) | 0.0039 | about 0.02 times | 0.192 to 0.245 times |
Within the haloacetonitriles, the abstract reports a difference between members of the group. “dibromoacetonitrile had the highest permeability while chloroacetonitrile had the lowest permeability”. This guide reports the group range and does not list individual compounds.
The abstract also states that the haloacetonitrile Kp values were “approximately 30 times that of CH”. That gap is large, and it is one reason the two compound groups give such different dermal ratios.
The pool ratios are higher than the average-population ratios. The authors write that the ratio “can vary markedly with chlorinated swimming pool exposures”. Pool water in the study is a different exposure from a home shower, so the pool figures should not be read as shower figures.
How the authors turned Kp into a dose
A Kp by itself does not say how much of a compound reaches the body. The authors combined the Kp values with a Monte Carlo simulation. This is a method that runs many random samples of people and exposure patterns, using stated ranges for body size, skin area and water use. The authors write that “Kp in vitro data is essential in estimating potential internal doses of in vivo dermal exposures”.
The simulation has built-in assumptions that matter for readers. One is about water intake. The authors state: “It was assumed that all of the consumed drinking water was unfiltered tap water to provide an estimate of the maximum ingestion dose”. That means the ingestion side of the ratio assumes unfiltered water. The paper does not model filtered water, so it does not show how a filter would change either side of the comparison.
A second assumption is about contact time. The authors write that the ratios assume “the Kp values determined are applicable to shorter water contact times”. Bathing and showering are short contacts, and the Kp values were measured under lab conditions. The paper does not test a shower at all. It models what the Kp values would mean for baths and pool visits.
The study also left one compound out. Trichloroacetonitrile was not included in the simulations because the authors could not determine a definitive Kp for it. The sources therefore do not give a dermal estimate for that compound.
Showers compared with baths
The 2011 paper includes a background statement about showers and baths, and it is a cited estimate, not a result of this study. The authors write that “Dermal exposure to water from bathing is expected to be even greater than from showering”, citing Brown and colleagues from 1984. They also summarize Brown’s work by saying that “an average of 64% of a total dose to lipophilic compounds in drinking water from showering is accounted for by dermal exposure and the rest from inhalation exposure”.
The same paper gives a second estimate for chloroform, the main THM in shower water. It says that “the daily dermal dose of chloroform from showering is approximately that of the daily ingestion dose from consuming two liters of tap water”. That estimate is attributed to earlier work by Jo and colleagues in 1990. The guide did not open that paper, so the figure is reported here only as the 2011 paper gives it.
The 2005 Environmental Health Perspectives study, covered in a separate section of this guide, measured chloroform in the exhaled breath and blood of seven subjects after showers. Its introduction notes that “Inhalation and dermal contact resulting from showering and bathing have been shown to be significant routes of exposure to THMs”. The 2005 abstract does not separate the skin route from the breathing route, so it cannot tell a reader how much of the chloroform came through the skin.
What the study does not say about skin effects
This is the part most readers need. The 2011 study measured how a chemical passes through skin in a lab. It did not measure what happens to skin afterward. The authors did not report redness, itching, dryness, rash, scaling or any other skin condition. They did not test hair. The sources do not say that chlorine dries out skin or damages hair, and this guide does not say so either.
The paper’s background explains the gap in the research. The authors write that “Skin is exposed to DBPs in water through bathing and swimming; however, dermal uptake of many DBPs has not been characterized”. They also state that “Potential dermal exposures to HANs and CH have not been reported”. This study addresses that gap for two compound groups. It does not address skin health.
The paper does mention toxicity in passing. It says that “These compounds have been reported to be mutagenic and teratogenic” in earlier studies the authors cite. That is an attributed statement about other work. The 2011 study did not test mutagenicity or teratogenicity, and it did not measure any effect on skin cells. Readers should not read the sentence as a skin finding.
Passing through skin and causing a skin problem are different questions. A compound can enter the skin without causing any visible change, and the sources in this guide do not measure whether the skin responds. For skin symptoms, talk to a dermatologist. For any health concern, talk to your doctor.
What the sources do not say
- The sources do not measure free chlorine or chloroform passing through skin. The compounds in the 2011 study are haloacetonitriles and chloral hydrate.
- They do not study living people, or any shower. The skin came from cadavers, under controlled lab conditions at 37 °C.
- They do not measure any skin condition, including irritation, dryness or rash, or any effect on hair.
- They do not test a filter, a shower head, or a water-saving device. The ingestion side of the ratio assumes unfiltered water.
- They do not give a safe level for any by-product in shower water.
- They do not give a dermal estimate for trichloroacetonitrile, because a Kp was not determined for it.
How we chose
This guide uses only two sources. The first is the 2011 Journal of Applied Toxicology study, which is the only source here that measures skin permeation. The second is the 2005 Environmental Health Perspectives study, which measured chloroform after showers and bathing in air, breath and blood. It is used for the exposure context, not for skin results. Both were opened and checked against saved copies of their text. Other sources were not used for claims in this guide. The guide does not rank products and does not recommend any shower head, hose or filter.
What we could not verify
The sources do not cover the following, so this guide makes no claim about them:
- Whether chlorine in shower water changes the condition of skin, hair or scalp in people.
- How the lab results compare with absorption through living skin during a real shower.
- Whether the lab Kp values apply to people with damaged, thin, or sensitive skin.
- Dermal exposure from showers in filtered water, or from any particular shower head or filter.
- Exposure in children, older adults, or people with skin conditions.
Where the sources give a figure, this guide reports it as the source gives it. The 2011 paper’s dermal ratios are model outputs, not measurements of a person.
FAQ
Does chlorine in shower water soak into the skin?
The 2011 study measured how some by-products pass through cadaver skin in a lab, and it found measurable permeability. It did not test chlorine itself, and it did not test a living person in a shower.
Does chlorine damage skin?
The sources do not say that. The 2011 study did not measure skin damage, and this guide makes no claim that chlorine damages skin or hair.
Are baths worse for skin absorption than showers?
The 2011 paper states that dermal exposure from bathing “is expected to be even greater than from showering”, citing an earlier study. The 2011 study did not compare baths with showers itself, so the statement is an attributed expectation.
Does a filter stop chlorine from reaching the skin?
Neither source tested a filter. The ingestion side of the study’s ratio assumed unfiltered water, so the paper gives no answer on filters.
What should I do if my skin is bothering me?
Talk to a dermatologist about skin symptoms. Talk to your doctor about any health concern. Neither source gives skin treatment advice, and this guide does not give it either.
Bottom line
The 2011 study shows that two groups of chlorine by-products pass through human skin in a lab at measurable rates, and it estimates that skin can be a significant route of exposure during baths and swimming. It does not show that these compounds harm skin, and it did not test a living person or a shower. Treat the numbers as a measure of passage through skin, not as a skin health result.
Sources
- Trabaris M, Laskin JD, Weisel CP. “Percutaneous Absorption of Haloacetonitriles and Chloral Hydrate and Simulated Human Exposures.” Journal of Applied Toxicology, 2011; 32(6): 387-394. https://pmc.ncbi.nlm.nih.gov/articles/PMC3199364/ (opened 2026-10-28)
- Gordon SM, Brinkman MC, Ashley DL, et al. “Changes in Breath Trihalomethane Levels Resulting from Household Water-Use Activities.” Environmental Health Perspectives, 2005; 114(4): 514-521. https://pmc.ncbi.nlm.nih.gov/articles/PMC1440773/ (opened 2026-10-28)
