Thyroid eye disease (TED) is triggered by an autoimmune attack on the tissue behind and around the eyes, most often in people with Graves’ disease. About 5 people per 100,000 develop it each year, with women affected roughly nine times more often than men. While the underlying autoimmune process is the root cause, specific factors can set it off or make it worse, and many of them are modifiable.
The Autoimmune Process Behind TED
TED starts when the immune system produces antibodies that target receptors on cells in the eye socket. These are the same receptors found on the thyroid gland, which is why TED almost always accompanies Graves’ disease. The antibodies stimulate specialized cells called orbital fibroblasts, which sit in the fat and muscle tissue surrounding your eyes. Once activated, these cells produce large amounts of hyaluronic acid, a substance that absorbs water and swells. The result is inflammation, tissue expansion, and the hallmark symptoms of TED: bulging eyes, redness, swelling, pain, and sometimes double vision.
What makes this process especially stubborn is that two key receptors on those orbital fibroblasts sit physically close together, within 40 nanometers, and form a signaling complex even before any antibody binds to them. This means the cellular machinery for inflammation is essentially pre-loaded and ready to fire. A stabilizing protein locks the two receptors together, so once antibodies arrive, the inflammatory response amplifies quickly.
Smoking Is the Strongest Modifiable Risk
Cigarette smoking is the single most powerful controllable trigger for TED. Smokers face roughly 7.7 times the odds of developing the disease compared to nonsmokers. The risk isn’t just about getting TED in the first place. The number of cigarettes smoked per day independently predicts how severe symptoms like eye bulging and double vision become. Smokers also respond more poorly to standard treatments, with studies showing that steroid therapy and radiation are less effective at reducing inflammation and improving eye movement in people who continue smoking.
The exact mechanism isn’t fully mapped, but smoking appears to ramp up inflammatory signaling molecules that directly affect the eye socket tissue. If you have Graves’ disease and still smoke, quitting is the single most impactful thing you can do to lower your risk of eye involvement.
Radioactive Iodine Treatment
Radioactive iodine (RAI) is a common treatment for an overactive thyroid, but it can trigger or worsen TED. In a landmark study, 15% of patients developed new or worsened eye disease after RAI, compared to just 3% of those treated with anti-thyroid medication alone. The risk was highest for people who already had some eye involvement: 24% of those with pre-existing eye symptoms experienced a flare after RAI, while 8% of those with no prior eye disease developed it for the first time.
The likely explanation is that destroying thyroid tissue with radiation releases a flood of thyroid antigens into the bloodstream, intensifying the autoimmune response. The good news is that a short course of oral steroids given alongside RAI essentially eliminated this risk in the same study. If your doctor recommends radioactive iodine and you have risk factors for TED, this preventive step is worth discussing.
Unstable Thyroid Hormone Levels
Both overactive and underactive thyroid states can fuel TED, but the real danger is fluctuation. Rapid swings in thyroid hormone levels, whether from inconsistent medication, dose changes, or untreated thyroid problems after RAI, are strongly associated with disease progression. This is true in both directions: unchecked hyperthyroidism and neglected hypothyroidism both push the eye disease forward.
This is why endocrinologists emphasize frequent thyroid level checks during the active phase of TED, which typically lasts one to three years. Keeping your thyroid function as stable as possible, even if it takes frequent medication adjustments, reduces the fuel that drives orbital inflammation.
Stress as an Immune Trigger
Severe psychological stress has long been suspected as a trigger for Graves’ disease itself, and there is growing evidence it can also provoke or worsen TED specifically. The biological pathway is plausible: chronic stress hormones like cortisol dysregulate the immune system over time, weakening the body’s ability to distinguish its own tissue from foreign threats. This loss of immune self-tolerance can tip a genetically susceptible person into active autoimmune disease.
Case reports have documented TED flares following major life events like bereavement, divorce, or job loss. While stress alone is unlikely to cause TED without the underlying autoimmune susceptibility, it appears to act as an accelerant on an already primed immune system.
Genetic Susceptibility
Not everyone with Graves’ disease develops eye involvement. Genetics play a significant role in who does. A specific immune system gene variant called HLA-DRB1*03 roughly doubles the odds of developing Graves’ disease compared to the general population. However, this gene variant doesn’t appear to specifically distinguish those who get eye disease from those who don’t, suggesting that other triggers layer on top of genetic susceptibility to determine whether the eyes become involved.
If you have a first-degree relative with Graves’ disease or TED, your baseline genetic risk is higher. That makes the modifiable factors, particularly smoking, thyroid stability, and treatment choices, all the more important to manage carefully.
Nutritional Factors: Selenium and Vitamin D
Selenium, a trace mineral with antioxidant properties, has the strongest nutritional evidence in TED. A randomized, placebo-controlled trial published in the New England Journal of Medicine tested selenium supplementation (200 micrograms daily) in 159 patients with mild TED over six months. Selenium significantly improved quality of life, reduced eye involvement, and slowed disease progression compared to placebo. The benefit persisted even after supplementation stopped. Selenium appears to work by neutralizing the oxygen free radicals that contribute to orbital inflammation.
Vitamin D deficiency has also been flagged as a potential contributor. In one study of TED patients, 20% were vitamin D deficient and another 31% had insufficient levels. The evidence here is less robust, based on small observational studies rather than controlled trials, but maintaining adequate vitamin D is reasonable given its broad role in immune regulation.
Other Risk Factors Worth Knowing
Age matters. Older adults with Graves’ disease tend to develop more severe TED when it occurs. Poorly controlled diabetes is another recognized risk factor, likely because elevated blood sugar worsens inflammation and impairs tissue healing throughout the body.
On the protective side, cholesterol-lowering statin medications have shown a striking association with reduced TED risk. A large retrospective study found that statin use was linked to a 44% reduction in the risk of developing eye bulging over five years of follow-up. An earlier observational study found a similar 40% reduction with at least 60 days of statin use in the preceding year. Statins have well-known anti-inflammatory effects beyond cholesterol lowering, which likely explains this association. These are observational findings rather than randomized trial results, so statins aren’t prescribed specifically for TED prevention, but for people already taking them for cardiovascular reasons, the potential eye benefit is a notable bonus.
Why Multiple Triggers Often Converge
TED rarely results from a single trigger acting alone. The typical pattern is a genetically susceptible person with Graves’ disease who encounters one or more additional hits: a course of radioactive iodine, continued smoking, a stressful life event, or a period of poorly controlled thyroid levels. Each factor adds fuel. This is why management focuses on controlling as many modifiable risks as possible simultaneously, stabilizing thyroid function, stopping smoking, supplementing selenium in mild disease, and carefully weighing the risks of radioactive iodine when eye involvement is present or likely.