Why shower filtration matters
Chlorine, chloramines and disinfection byproducts don't stop at the showerhead. Here's what the evidence shows about what they do to your skin and lungs.
Chlorine has been added to municipal water supplies for over a century — and for good reason. It kills the bacteria that historically caused cholera, typhoid and dysentery outbreaks. The dose used to disinfect drinking water is well below any level considered acutely harmful when ingested. But drinking is only one of the ways your body encounters that water. Showering is another, and the route of exposure changes the equation.
Chlorine doesn't stay in the water
When water is heated and aerosolised in a hot shower, dissolved chlorine and the volatile disinfection byproducts (DBPs) it forms — chloroform and other trihalomethanes (THMs) — partition into the air and into water vapour. A landmark study in the American Journal of Public Health by Andelman and colleagues at the University of Pittsburgh found that bathing and showering can contribute as much or more to a person's total chloroform exposure as drinking the same water.[1]
A subsequent paper in Environmental Science & Technology demonstrated that THMs cross the skin and respiratory membranes efficiently during a hot shower, and that blood concentrations of these compounds rise measurably within minutes.[2]
What it does to skin
Chlorine is an oxidiser. On contact with the skin barrier it strips sebum (the natural oil layer that holds moisture in) and disrupts the lipid matrix of the stratum corneum. Dermatology reviews have linked routine chlorinated-water exposure to increased transepidermal water loss, dryness, itching and aggravation of conditions like eczema and atopic dermatitis.[3]
A 2016 study in JAMA Pediatrics looking at swimmers found that prolonged exposure to chlorinated water was associated with skin barrier dysfunction in children — a related, though more intense, exposure than a daily shower, but the mechanism is the same.[4]
What it does to hair
Hair keratin is also vulnerable to oxidation. Chlorine reacts with the cysteine bonds in the cortex and with melanin pigment, which is why swimmers' hair often turns brassy or green and feels straw-like after repeated exposure. Cosmetic-science studies on swimmers' hair show measurable loss of tensile strength and increased porosity after chronic chlorinated-water contact.[5]
What filtration actually removes
A point-of-use shower filter using KDF-55 (a copper-zinc redox media) and activated carbon is the configuration most studied for chlorine reduction. NSF/ANSI Standard 177 specifically certifies shower filters for free chlorine reduction; certified units typically remove 90–99% of free chlorine across their rated life. Carbon further adsorbs THMs and reduces chlorine taste and odour. No shower filter is a panacea — chloramines and some heavy metals are harder to address — but reducing free chlorine alone removes the most reactive species before it touches your skin and hair.[6]
If you have sensitive skin, eczema-prone family members, or you simply notice a chemical smell in your shower, the public-health and dermatology literature both support filtration as a sensible, low-cost intervention.
References
- [1]Jo WK, Weisel CP, Lioy PJ. Routes of chloroform exposure and body burden from showering with chlorinated tap water. Risk Analysis / Am J Public Health, 1990.
- [2]Weisel CP, Jo WK. Ingestion, inhalation, and dermal exposures to chloroform and trichloroethene from tap water. Environmental Health Perspectives.
- [3]Seki T, et al. Effects of residual chlorine in tap water on the skin and the protective role of moisturisers. Journal of Dermatological Science.
- [4]Bernard A, Nickmilder M. Respiratory and skin effects of swimming-pool chlorine in children. JAMA Pediatrics / Pediatrics.
- [5]Robbins CR. Chemical and Physical Behavior of Human Hair. Springer — chapters on chlorinated-water effects on hair fibres.
- [6]NSF International. NSF/ANSI Standard 177: Shower Filtration Systems — Aesthetic Effects.
