What’s Actually Causing Your Thyroid Disease

Genetics. Having the genes doesn’t mean you get the disease. Something has to trigger it.

Environmental toxins. The longest section below, because it’s the one you control.

Iodine, too little or too much. Both cause disease.

Pregnancy and the postpartum window. Missed constantly.

Medications and treatments. Radiation, chemo, and several common prescriptions.

Selenium and vitamin D status. The two nutrients with real evidence behind them.

H. pylori. A stomach bacteria with the strongest causal signal of any infection.

Gut permeability and bacterial overgrowth.

Chronic stress and early-life adversity.

That’s the whole list. Now here’s what to do with it.

Identical twins share every gene. When one twin has Hashimoto’s, the other has it just over half the time. Same DNA, opposite outcome, in nearly half of those pairs.

That gap is the whole story. You inherit the susceptibility. What switches it on is diet, stress, infection, and exposure, and those are things you touch every single day.

This is why knowing your epigenetics matters. Your genes tell you what you’re susceptible to. Your epigenetics tell you what’s actually being expressed and what you can do about it, and that’s the part almost nobody gets tested.

Your thyroid pulls iodine out of your blood through a doorway that isn’t picky. It lets in anything shaped close enough. A lot of what you spray, wear, wash with, and drink is shaped close enough.

This is the highest-frequency exposure in your house. Not the biggest single dose. The one you repeat every morning for thirty years.

Fragrance. One word on a label, and it legally covers dozens of undisclosed chemicals. Phthalates are frequently among them. Meeker and Ferguson found phthalate exposure associated with lower thyroid hormone in national health survey data.

Where it’s hiding: perfume, cologne, body spray, deodorant, lotion, shampoo, conditioner, hairspray, shaving cream, hand soap.

What to use instead: anything labeled fragrance-free, which is different from unscented. Unscented can mean a masking fragrance was added. Scan a product with the Yuka or Think Dirty app before you buy it, or look it up in the EWG Skin Deep database. Start with the products that stay on your skin all day, deodorant and lotion, before you worry about the ones that rinse off.

Triclosan. Antibacterial hand soap and some toothpaste. Plain soap works.

Nonstick cookware. PFAS, the forever chemicals. The C8 Health Project followed tens of thousands of people with contaminated water in the Ohio River Valley and found a link to thyroid disease. Findings across studies have been mixed, and I’ll say that plainly, but the exposure is close to universal.

What to use instead: cast iron, stainless steel, carbon steel, or enameled cast iron. If a pan is scratched or flaking, it goes in the trash today, not after you replace it.

Canned food. BPA in the lining attaches to your thyroid hormone receptor and sits there without doing the job. BPS and BPF, the replacements, are structurally similar.

What to use instead: glass jars, cartons, or dried beans you cook yourself. Tomatoes are the one worth switching first, because acidity pulls more out of the lining.

Plastic food storage. Heat is the multiplier. Microwaving in plastic and running it through a hot dishwasher both accelerate leaching.

What to use instead: glass containers. Never microwave in plastic, including takeout containers and the film over frozen meals.

Receipts. Thermal paper is coated in BPA and it transfers through your fingertips. Decline the receipt or take the email.

Scented detergent, fabric softener, and dryer sheets. Fragrance again, and this time you’re wearing it for the next eighteen hours against your skin, and sleeping in it.

What to use instead: fragrance-free detergent and wool dryer balls. This swap is cheap, easy, and it covers your sheets, your towels, and every piece of clothing you own.

Air fresheners, plug-ins, and scented candles. Same problem, aerosolized into a room you breathe.

What to use instead: open a window. Beeswax or soy candles with a cotton wick and no fragrance oil. Simmer citrus peel and rosemary on the stove if you want the house to smell like something.

Flame retardants. Furniture foam, carpet padding, electronics, and car interiors. These come out of the product and settle into house dust, and dust is how most of it gets into you. Not your food. Your floor.

What to use instead: you can’t replace a couch this weekend, so manage the dust instead. Vacuum with a HEPA filter. Damp dust rather than dry, which just relocates it. Take shoes off at the door. Wash hands before eating, which matters most for kids who are on the floor all day. When you do buy furniture, look for a TB117-2013 label stating no added flame retardants.

Perchlorate from rocket fuel and fertilizer, nitrate from agricultural runoff, and PFAS all show up in drinking water. Blount and colleagues found perchlorate associated with lower thyroid hormone and higher TSH in over a thousand women, and the effect was much larger in women whose iodine was already low. Low iodine plus perchlorate is a different situation than either one alone.

What to use instead: look up your zip code in the EWG Tap Water Database first, so you know what you’re filtering for. Reverse osmosis handles the widest range including perchlorate and nitrate. A carbon block filter certified to NSF/ANSI 53 for PFAS is the cheaper option. A basic pitcher filter is mostly for taste and won’t touch these.

The Agricultural Health Study followed more than 16,000 farm women and found associations between specific pesticide use and thyroid disease, with the clearest signals from organochlorines and a class of fungicides that breaks down into a documented thyroid toxicant.

You’re not farming. But the service that comes every six weeks, the bag in the garage, and the strip along the sidewalk are the same category at a lower dose repeated for twenty years.

What to use instead: ask your lawn service for the product list and look it up, which most people never do and which changes the conversation immediately. Corn gluten meal works as a pre-emergent. Mow high and overseed in fall, because thick grass crowds out weeds better than anything you spray. Pull what’s left by hand.

Glyphosate gets named in every article like this one. The direct human thyroid data on it is thin, and I’d rather tell you that than pad the list.

Pesticide residue. Buy organic for the produce that carries the most, and use the EWG Dirty Dozen list rather than trying to buy everything organic, which is how people give up.

Fish. Mercury and PCBs concentrate in large, long-lived, fatty fish. Smaller fish carry far less. Salmon, sardines, anchovies, and mackerel give you the omega-3s without the same load.

Cured meat. Nitrate. Occasional is different from daily.

You don’t have to. Nobody does this all at once, and the people who try usually quit by the end of the week.

Here’s the actual approach. Wait until you run out of something, then replace it with the non-toxic version. Your shampoo runs out, buy the fragrance-free one. Your detergent runs out, switch it. A pan gets scratched, replace it with cast iron. Pick two or three things you were going to buy anyway and just buy them differently.

That’s it. Over a year you’ll have replaced most of what matters and you won’t have thrown anything away or spent a weekend on it.

Some of what causes hypothyroidism comes from a bottle or a machine, prescribed for a good reason, and nobody follows up on the thyroid afterward.

Radiation to the head, neck, or upper chest. The thyroid sits directly in the field. This is dose-dependent and well established. Hodgkin lymphoma survivors treated with mantle field radiation have among the highest rates of any group, and the damage can show up decades later.

Total body irradiation before a stem cell transplant carries the same risk.

Childhood cancer survivors are the population where this gets missed most. A child treated at seven may develop hypothyroidism at twenty-two, in a different city, with a different doctor, who has no idea what happened fifteen years earlier. If you or your child had radiation anywhere near the neck, thyroid labs belong in the yearly bloodwork for life.

Radioactive iodine. Used to destroy an overactive thyroid, so the hypothyroidism is expected. Not a complication, a design.

Tyrosine kinase inhibitors, sunitinib especially, cause hypothyroidism at high rates.

Immunotherapy. Checkpoint inhibitors are one of the most common causes of new thyroid disease in oncology right now. Combination therapy carries the highest risk. The usual pattern is a brief overactive phase followed by permanent hypothyroidism.

Interferon and interleukin-2 can trigger autoimmune thyroiditis.

Bexarotene suppresses TSH centrally.

Lithium. The clearest one on this list. Concentrates in the thyroid and blocks hormone release. Anyone on lithium should have thyroid labs monitored, and most do.

Amiodarone. A heart rhythm drug carrying an enormous iodine load. Causes both underactive and overactive thyroid, sometimes in the same person.

Anticonvulsants. Carbamazepine and phenytoin speed up hormone clearance.

Estrogen and oral contraceptives. Raise binding proteins. Total hormone looks off, free hormone is usually fine. This is why free levels matter and total levels mislead.

Absorption blockers. Calcium, iron, PPIs, and coffee all interfere with thyroid medication. Take levothyroxine on an empty water-only stomach, and separate it from calcium and iron by four hours. A lot of “my medication isn’t working” is this.

I’ve watched this pattern for twenty years, and I’m going to describe it before I show you the data, because the data doesn’t say exactly this and I won’t pretend it does.

The women who come to me with Hashimoto’s are, over and over, the ones who’ve spent years managing everyone else’s comfort. Walking on eggshells. Reading the room before speaking. Swallowing the thing they wanted to say because saying it would cost more than not saying it.

There’s no study on that. Anyone who tells you otherwise is selling you something.

But there’s a real literature underneath it, and it’s stronger than most people know.

Adverse childhood experiences. The ACE study asked adults about ten categories of childhood adversity, things like abuse, neglect, a parent with addiction, or a household where you learned early that your needs weren’t the priority. Dube and colleagues found that as ACE score went up, hospitalization for autoimmune disease in adulthood went up with it, step by step. Not thyroid alone. Autoimmune disease broadly.

If you’ve never taken it, the ACE questionnaire is ten questions and it’s free online. Knowing the number doesn’t fix anything. It does explain a lot of things people have been blaming themselves for.

PTSD. O’Donovan and colleagues followed 666,269 veterans and found PTSD associated with significantly increased risk of autoimmune disease, thyroiditis included. That’s the best-designed study in this space, and the number of people in it is why.

Emotional suppression. Chapman and colleagues followed a national sample and found people who habitually suppressed emotion had higher all-cause mortality. That’s the closest research has come to the pattern I described at the top, and it isn’t thyroid-specific.

What’s happening physically. Chronic stress raises cortisol. Cortisol suppresses TSH and shifts how your body converts storage thyroid hormone into the active form, pushing more of it down an inactive path. Cortisol also affects the lining of your gut. That’s documented physiology, and it’s the honest bridge between a life spent braced and a thyroid that stops keeping up.

And the part that complicates all of it. Hypothyroidism itself causes fatigue, flat affect, slowed thinking, depression, and sometimes changes to the vocal cords that alter the voice. So a woman who’s gone quiet may not have gotten sick from silence. She may be showing you the illness.

I’ve sat with both. I can’t always tell you which came first, and I wouldn’t trust anyone who says they can.

Iodine, in both directions. Too little and too much both cause disease. When countries added iodine to salt, hypothyroidism dropped and autoimmune thyroiditis rose.

Pregnancy and postpartum. Postpartum thyroiditis affects 5 to 10% of women, closer to 20% in higher-risk groups. It gets missed constantly, because everyone assumes a new mother is tired for obvious reasons.

Selenium status. Best nutrient evidence there is. It lowers antibodies in trials. What it hasn’t been shown to do is change who goes on to develop full disease, and that distinction matters.

Vitamin D. Consistently low in people with thyroid autoimmunity, with a modest antibody effect when corrected.

H. pylori. A stomach bacteria, and the only infection with genetic-inference evidence pointing toward cause rather than coincidence.

Gut permeability and bacterial overgrowth. Bacterial overgrowth shows up in about a third of hypothyroid people compared to 15% of controls. Low thyroid also slows the gut down, so this one likely runs in both directions.

Print this. Bring it to your appointment.

Ask for all six by name. Most providers run TSH alone.

MARKER LAB “NORMAL” 🟢 OPTIMAL TSH 0.45 to 4.50 mIU/L 1.0 to 2.5 mIU/L Free T3 2.0 to 4.4 pg/mL 3.2 to 4.0 pg/mL Free T4 0.8 to 1.8 ng/dL 1.0 to 1.5 ng/dL Reverse T3 Not routinely run Under 15 ng/dL TPO Antibodies Under 35 IU/mL Under 9 IU/mL TG Antibodies Under 20 IU/mL Under 9 IU/mL

Normal = Common. Optimal = Healthy.

TSH. The signal from your brain telling the thyroid to work harder. Rising TSH means your brain is yelling. It’s the only test most people get, and it’s the last one to change.

Free T4. Storage hormone. Mostly inactive until converted.

Free T3. The active hormone. This is the one your cells use. You can have a perfect TSH and low T3, and you will feel every bit of it.

Reverse T3. The inactive form. Rises with stress, illness, low calorie intake, and inflammation. Not run by most labs and not endorsed by conventional guidelines, so know that going in.

TPO and TG antibodies. The autoimmune markers. These can be positive for years before TSH moves. A normal TSH with positive antibodies is not a normal thyroid, it’s an early one.

Thyroid function depends on them, and a thyroid panel read without them is missing half the picture.

MARKER 🟢 OPTIMAL Ferritin 50 to 100 ng/mL Vitamin D 50 to 80 ng/mL B12 Over 500 pg/mL, ideally 700+ hs-CRP Under 1.0 mg/L RBC Magnesium 5.5 to 6.5 mg/dL Fasting Insulin Under 5 µIU/mL

One thing that will wreck your results. Stop biotin for three to five days before the draw. High-dose biotin in hair, skin, and nail supplements interferes with the assay and can make thyroid labs look wildly wrong in either direction. Most people are never told this.

👉 Say this to your provider: “I’d like a full thyroid panel including Free T3, Free T4, and thyroid antibodies, not just TSH.”

You inherited the susceptibility. You didn’t inherit the outcome, and the space between those two things is where you live.

If you want to go deeper on how to actually heal your thyroid, that’s what we do inside Optimal Not Normal: skool.com/optimal-not-normal-1374

And on Thursday, paid subscribers get the tool to read their own thyroid labs, so you finally know whether you’re optimal or just normal.

This post is for educational purposes only and does not constitute medical advice. Please work with your own healthcare provider for personalized care.

The most radical act in a sick society is to heal yourself — and then gently help others heal too.

— Dagmara