What are the side effects of iodine in water?

January 9, 2026 •

4 min read

According to the National Institutes of Health, taking high doses of iodine over time can be harmful, with impacts on the thyroid gland being a primary concern. This article explores what are the side effects of iodine in water, which can occur from consuming naturally high-iodine water or using iodine-based purification methods.

Quick Summary

Excessive iodine intake from water can lead to thyroid dysfunction, including goiter, hypothyroidism, or hyperthyroidism, in susceptible individuals. It can also cause gastrointestinal distress and allergic-like reactions.

Key Points

Thyroid Dysfunction: Excess iodine from water can cause or worsen thyroid conditions like hypothyroidism, hyperthyroidism, and autoimmune thyroiditis.
Gastrointestinal Distress: High levels of iodine intake can lead to immediate symptoms such as a metallic taste, nausea, vomiting, and stomach pain.
Hypersensitivity Reactions: Although a true allergy to elemental iodine is a myth, reactions to iodine-containing compounds can cause rashes, hives, swelling, and even anaphylaxis.
Chronic Exposure Risks: Long-term consumption of naturally high-iodine water, especially above 100 µg/L, is linked to a higher risk of autoimmune thyroid disorders.
Vulnerable Populations: Pregnant women, infants, and individuals with pre-existing thyroid conditions are more susceptible to the adverse effects of excessive iodine intake.
Water Purification Precaution: Iodine tablets are intended for short-term, emergency use, not prolonged consumption, due to the risk of toxicity.
Mitigation Strategies: Using alternative purification methods like chlorine tablets or physical filters (e.g., reverse osmosis) can prevent excessive iodine exposure from water.

The Body's Reaction to Excessive Iodine

Iodine is a necessary trace mineral for the human body, vital for producing thyroid hormones that regulate metabolism, growth, and development. While most people get sufficient iodine from iodized salt and food, excess intake can be harmful. This excess can come from naturally occurring high iodine levels in groundwater or from the overuse of iodine-based water purification tablets for an extended period. A healthy thyroid can usually adapt to minor fluctuations in iodine intake, but persistently high levels can disrupt this delicate balance. The relationship between iodine intake and thyroid health is often described as a 'U-shaped curve,' meaning both too little and too much can cause problems.

Thyroid Health and Iodine Overload

The most significant side effects of excessive iodine are on the thyroid gland. Prolonged, elevated intake can increase the risk of thyroid disorders, including:

Hypothyroidism: An underactive thyroid that doesn't produce enough hormones. Symptoms include fatigue, weight gain, increased sensitivity to cold, and a swollen thyroid gland (goiter).
Goiter: An enlarged thyroid gland, which can result from both iodine deficiency and excess, as the gland struggles to adapt to imbalanced intake.
Autoimmune Thyroiditis: Studies have linked prolonged exposure to high levels of iodine in drinking water to an increased risk of autoimmune thyroid disorders (AITDs). In individuals with a predisposition to autoimmune issues, high iodine levels can trigger or worsen the condition.
Hyperthyroidism: In populations with pre-existing iodine deficiency, a sudden increase in iodine can induce hyperthyroidism (an overactive thyroid), especially if nodules have developed.

Acute and Sub-chronic Symptoms of Iodine Toxicity

In addition to long-term thyroid issues, ingesting very large amounts of iodine can cause acute toxicity, though this is less likely from regular drinking water and more from accidental ingestion of a concentrated solution. More moderate or prolonged exposure, such as from continued use of water purification, can cause sub-chronic issues.

Some common side effects include:

Metallic or brassy taste in the mouth.
Burning sensation in the mouth and throat.
Stomach upset, nausea, vomiting, or diarrhea.
Increased salivation.
Soreness of teeth and gums.
Skin rashes.

Hypersensitivity and 'Iodine Allergy'

While a true allergic reaction to elemental iodine is considered medically impossible, hypersensitivity reactions to iodine-containing compounds are documented. These are often reactions to other components in the substance. Symptoms of a hypersensitivity reaction can range from a mild rash to more severe, life-threatening conditions like anaphylaxis.

List of potential hypersensitivity symptoms:

Itchy rash or hives.
Swelling of the tongue or throat.
Shortness of breath.
Fever.
Headache.
In rare cases, anaphylactic shock.

Comparison of Different Iodine Exposure Sources

The risks associated with iodine exposure from water can vary significantly depending on the source. Here is a comparison of two primary routes of exposure.


Aspect	Naturally High-Iodine Groundwater	Iodine Water Purification Tablets
Source	Geologic processes near coastal areas or brines	Active ingredient (e.g., potassium iodide) in tablets
Typical Exposure	Chronic, long-term exposure from daily drinking water	Short-term, intermittent use for camping or emergency
Primary Risk	Thyroid disorders, especially AITD, over time	Acute GI distress or hypersensitivity reactions from high single doses
Affected Populations	Residents in endemic high-iodine areas	Travelers, military, or individuals in emergencies
Risk Management	Water source modification or alternative sources	Use for short duration only and follow dosage instructions

Recommendations for Managing Iodine in Water

For those exposed to high iodine levels in their water, either from natural sources or through disinfection, several measures can be taken to mitigate risk.

Test Your Water: If you suspect high natural iodine levels, a water test is the first step. For areas with endemic high-iodine water, monitoring is crucial.
Filter Your Water: Consider using a reverse osmosis or deionization filter, which can effectively remove various mineral ions, including iodide. Standard carbon filters are not effective for this purpose.
Use Alternative Disinfection: For emergency water purification, consider chlorine-based tablets or filters, which do not contain iodine. Limit the use of iodine-based tablets to short durations only.
Monitor Thyroid Health: Individuals with pre-existing thyroid conditions, pregnant women, and young children should be particularly cautious. Regular monitoring of thyroid function is recommended for those with long-term exposure to high-iodine water.
Be Aware of Symptoms: Pay attention to any signs of thyroid dysfunction or other side effects and consult a healthcare provider if concerns arise. The sooner problems are addressed, the better the outcome.

Conclusion

In conclusion, while iodine is an essential element for human health, excessive exposure, particularly from drinking water, carries significant risks. The most concerning side effects of iodine in water involve the thyroid gland, with prolonged, elevated intake increasing the likelihood of hypothyroidism, goiter, and autoimmune thyroid disorders in susceptible individuals. Acute gastrointestinal distress and allergic-like reactions are also possible with high doses. Individuals using iodine-based water purification should do so for short-term emergency situations, while those in areas with naturally high water-iodine should consider water filtration and regular health monitoring to ensure safety. For further information and guidelines on safe iodine intake, consult the NIH Office of Dietary Supplements.

Frequently Asked Questions

Yes, drinking water with excessive levels of iodine can cause thyroid problems, including hypothyroidism, hyperthyroidism, and goiter. For susceptible individuals or with chronic exposure, it may also increase the risk of autoimmune thyroid disorders.

Using iodine tablets for short-term emergency water purification is generally safe. However, prolonged use, such as for more than a few weeks, is not recommended and can increase the risk of adverse health effects due to excessive iodine intake.

Acute toxicity from a large dose of iodine can cause a burning sensation in the mouth and throat, a metallic taste, fever, abdominal pain, nausea, and diarrhea.

While an allergy to the element iodine is not possible, hypersensitivity reactions can occur in response to iodine-containing compounds. Symptoms may include a rash, hives, swelling, and in rare cases, anaphylaxis.

The most reliable way to determine if your water has high iodine levels is to have it professionally tested. High iodine concentrations are often associated with specific geographic regions with iodine-rich soil or groundwater.

Individuals most at risk include pregnant women, infants, young children, and people with pre-existing thyroid conditions, especially those with autoimmune thyroid disease or iodine deficiency.

Reverse osmosis and deionization filtration systems are effective at removing excess iodide from drinking water. Using bottled water or an alternative purification method like a non-iodine-based purifier are other options.