A Daily Chemical Exposure, Documented for 50 Years, Missing From Every Testosterone Protocol

By Dan Reese  |  September 17, 2026

“In range.”

That’s what he said. Bottom of the range — but in range. Which is the medical way of saying come back when it’s worse.

Seven minutes. I timed the appointment, because that’s what I do. I measure things.

I was told to lose a little weight and get more sleep. I sleep seven and a half tracked hours. I lift four days a week. He didn’t ask.

I’m thirty-eight. I own the steel bottle. I read ingredient labels the way other men read box scores. I tested low on vitamin D once and fixed it in a month, because that’s the deal I run with myself: find the problem, fix the problem.

The results don’t match the effort. I’ve done everything on the list. So the question that followed me out of that parking lot: what isn’t on the list?

You Already Know Something Is Doing This

I’d seen the charts. Testosterone levels in American men have been sliding for decades — a population-level decline that shows up independent of age, which means a man of 35 today is working with less than his father had at 35, and meaningfully less than his grandfather. (Travison et al., J. Clin. Endocrinol. Metab., 2007)

My grandfather never optimized anything in his life, and he had more to work with at 60 than most 35-year-olds do now.

That gap has a shape, and I suspected what filled it — probably the same things you do. I switched to a steel bottle years ago. I stopped microwaving plastic. I filter my drinking water. I’d read the words microplastics and endocrine disruptors a hundred times, in a hundred articles that all ended the same way — vaguely, with nothing to actually do.

Here’s what none of those articles said: I was right. Right to filter, right to switch, right to distrust the defaults. I was just never told which room to check.

Chlorine Does Its Job. Then It Does Something Else.

Chlorine is in your water for a good reason: it kills things, and it has done that job so well for a century that waterborne disease is something you never think about. But chlorine stays reactive after its work is done. On the way to your house it meets organic matter and reacts with it, forming a family of by-product compounds called trihalomethanes (THMs). That’s the last time you’ll need the word — from here on, think of it as what chlorine leaves behind.

The important part: these by-products are not forming in your bathroom. They form in the distribution system, in the hours the water spends in the pipes between the treatment plant and your street, and they arrive at your shower arm already made. Hold onto that fact — it matters later.

In cold water, they mostly stay in the water. Wash your hands, fill a glass — very little reaches the air. Heat changes that. These compounds are volatile, and a hot shower moves them out of the water and into the steam. The steam is the delivery system, and you’re standing inside it. (Andelman, Environ. Sci. Technol., 1985)

Heat does a second thing at the same time: it changes your skin. Warm skin is measurably more permeable than cool skin — more crosses at 104°F than at 95°F. Same water, same ten minutes, more of it in you.

So which route matters more — breathing it, or absorbing it? Researchers answered that directly: volunteers showered in wetsuits to isolate the skin from the lungs, and the two routes came out roughly equal. (Jo, Weisel & Lioy, Risk Analysis, 1990) That finding changes the math — every estimate built on inhalation alone was counting half the exposure.

And here is the sentence this article is built on. Drink these compounds and your liver processes them before they reach circulation — that is what a liver is for. Breathe them, or absorb them through skin, and there is nothing in between. They enter the blood directly.

The dose tracks like a dose. In a controlled study, ten minutes of showering in water carrying chloroform — the most common of these by-products — at 64 µg/L raised blood levels by roughly 190 ng/L. Double the concentration in the water, and blood levels roughly double. (Backer et al., J. Expo. Anal. Environ. Epidemiol., 2000)

Then I Did the Math on My Own Bathroom

Ten minutes. Every morning. Hot water, door closed, fan off — nobody runs the fan.

I moved in at twenty-six. Call it twelve years. I ran the math three times because I kept not liking the answer: four thousand three hundred showers. Twenty-five gallons each. More than a hundred thousand gallons of hot water, turned to steam in a closed room, with me standing in the middle of it — breathing it in and taking it through the largest organ I own, both routes at once, every single day.

I filter the two liters I drink. I was proud of that. Two liters filtered. Twenty-five gallons a morning, not.

And here’s the part that actually got me: nobody hid it. My water utility publishes its by-product levels every single year — federal law. It’s in the annual water-quality report I’ve been throwing away unopened for twelve years. Then I paid a doctor to tell me to get more sleep.

The Fan Doesn’t Fix It

My first thought was the cheap one: run the fan, crack a window.

Researchers measured that too. Cutting bathroom air concentrations by around 75% moved blood levels by about 2–3%. (see references) Not seventy-five. Two to three.

And ventilation only ever addressed the air. The fan was never going to touch the half of the exposure that comes through skin. The math killed the free fix in one afternoon.

What I’m Not Going to Tell You

First, what the science actually found. No hedging.

Researchers fed rats the four by-products chlorine makes. One at a time. All four dropped their testosterone within a week. Four for four. Not one bad apple — the whole family. (Potter et al., Cancer Letters, 1996)

Then the humans. 1,199 healthy men. Scientists measured these exact chemicals in their blood — blood, not a survey about shower habits. The result: the more of it in a man’s blood, the lower his sperm count and the weaker his swimmers. And it scaled. More chemical, worse numbers. (Chen et al., Environment International, 2020)

One more, because you deserve the whole hand. A third study measured these chemicals against testosterone itself, in men. It found a dip — pointing down, but not big enough to bank on. I’m telling you that myself, because you’d find it anyway, and a page that hides its weakest card is a page you shouldn’t trust. (Zeng et al., Environment International, 2013)

So here’s the line. I won’t tell you chlorine is why your T is low. Nobody can tell you that. Any brand that promises it is lying to you for money.

But I don’t need to promise it. Three facts, all published: this stuff drops testosterone in rats — every version of it. It tracks with worse numbers in over a thousand men. And it’s entering your blood every hot shower, with nothing in between. Connect those dots however you want. I connected mine — and the rest of this page is what I did about it.

So I Went to Buy a $30 Shower Filter

My next move was the obvious one: search, shower filter, thirty dollars, done.

That’s when I found the detail this entire article exists to tell you.

The standard media inside almost every shower filter on the market is KDF-55 and calcium sulfite. Both are real technologies and both genuinely work — on chlorine. KDF converts it through a redox reaction; calcium sulfite chemically reduces it.

Neither one adsorbs a compound that has already formed.

Go back to the mechanism for a second: the by-products this article is about don’t form in your bathroom. They form in the pipes, and they arrive at your shower pre-made. A filter built to neutralize chlorine is intercepting the ingredient — after the cooking is done.

Only activated carbon adsorbs the finished compounds. It’s what municipal treatment plants themselves use for exactly this class of chemical. (EPA treatment guidance — see references)

So the $30 filter does something real: it removes the chlorine you can smell. And it leaves the thing you just read four hundred words about.

I want to be fair here, because it took me a while to see it: this isn’t the filters being bad. The whole category was designed for the chlorine you can smell, not the by-products you absorb. Nobody built for this, because nobody was selling this problem.

Which means the fix isn’t throwing KDF out. KDF does its job. The fix is adding the one media the category left off.

The Standard, Not the Object

Nobody will ever see it. No logo, nothing to post, no one to impress. A shower filter might be the least visible purchase a man can make.

Which is exactly the filter on who makes it. The visible stuff gets done for the audience — the watch, the truck, the physique. The invisible stuff gets done by men who are keeping score with themselves. Sleep handled. Training handled. Food handled. Drinking water handled. Exposure is the next line on that list, and it’s still nearly empty — because there’s no applause on it.

And I’ll say where I was plainly: out of levers. Sleep, training, diet, supplements — dialed, for years. The next conversation on the road I was on was TRT, and I’m thirty-eight. I wasn’t ready to open a door that doesn’t close while there was still a default I’d never once checked.

This was the one lever left that asked nothing of me. No discipline. No compliance. No 6 a.m. step to remember. Equipment, installed once, working every morning I forget it exists.

Why It’s Two Pieces of Hardware

The system I installed is two pieces, and the reason why is the chemistry lesson above.

Carbon works by adsorption — the compounds bind to its surface as water passes through. Adsorption needs two things: mass and contact time. An in-head cartridge is the smallest carbon configuration that exists; at full flow, water spends roughly one second inside it.

So the first piece is an inline canister that sits upstream, on the tap itself — the first thing the water meets. Inside is the media — KDF among it, alongside antibacterial balls and vitamin C — plus the part the category stops short of: activated carbon fibre, several times the carbon of an in-head cartridge, wrapped in sediment cotton. Every drop passes through the full stack before the water reaches the head.

The second piece is the showerhead, which carries a second stage of activated carbon fibre plus sediment filtration. Two carbon passes, not one.

That’s the whole design. Carbon at the tap, because that’s where mass and contact time live; carbon again in the head, as the second pass. It’s the same media municipal treatment plants use for chlorine and its by-products — a category fact you can verify in thirty seconds, which matters more to me than any percentage a brand could print.

The Three Questions I Had Left

“Water touches the filter for a second. That can’t be enough.” True — for an in-head cartridge, and it’s exactly why this system is two pieces. The canister is where mass and contact time live; the head is the second pass. The objection turned out to be the design brief.

“Shouldn’t I just do whole-house filtration?” I priced it: $1,000–4,000 plus a plumber, and structurally impossible if you rent. The volatile exposure this article is about happens in one room — the one where the water is hot. The shower is the choke point.

“A showerhead can’t fix my hormones.” Correct, and I already told you so myself. That claim isn’t on this page. One documented exposure, removed. That’s the whole transaction.

The Photograph That Ended My Research

I could give you more chemistry. Instead: what a cartridge looks like new, and what an identical one looks like after three months of daily showers, same surface, same light.

Everything on the used one came out of water that looked completely clear. That’s the entire pitch. The rest of this page was just the explanation.

Twelve Years of Mornings

Ten minutes at a time, both routes at once — that was my exposure. Yours is however long you’ve lived at your address.

The system is the PureGuard two-stage: canister, head, both cartridges in the box, installed by hand in about a minute. If the used cartridge doesn’t tell its own story in ninety days, send it back.

90-day money-back guarantee · free shipping · installs by hand, no plumber

Dan Reese

Dan Reese covers environmental exposure and men’s health. He has read his city’s water quality report more times than anyone should.