Can using 2% iodine (iodine) on teeth cause hyperthyroidism (an overactive thyroid gland) symptoms, especially if taking multivitamins (multivitamin supplements)?

Can Topical Iodine Application on Teeth Cause Hyperthyroidism?

Yes, topical application of 2% iodine solution on teeth can potentially cause hyperthyroidism symptoms, particularly when combined with iodine-containing multivitamins, as iodine is well-absorbed through mucous membranes and can lead to excessive systemic iodine exposure.

Understanding the Mechanism

Topical iodine disinfectants represent a well-recognized source of excessive iodine exposure that can trigger thyroid dysfunction 1. The oral mucosa is highly vascular and permits significant systemic absorption of iodine, even from topical applications 1. When this exposure is combined with iodine-containing multivitamins, the cumulative iodine load can exceed safe thresholds and precipitate thyroid dysfunction 2, 3.

Iodine excess can trigger hyperthyroidism through two primary mechanisms:

• In individuals with pre-existing autonomous thyroid nodules or subclinical thyroid disease, excess iodine provides substrate for unregulated thyroid hormone synthesis, leading to iodine-induced hyperthyroidism 1, 4, 5
• Even in previously healthy individuals, excessive iodine can overwhelm normal thyroid autoregulatory mechanisms and induce thyrotoxicosis 6, 7

Clinical Context and Risk Factors

The patient's risk is elevated by several factors:

• Multiple exposures: Two separate applications (October 9 and Thanksgiving 2025) represent repeated iodine loading 1
• Concurrent multivitamin use: Many multivitamins contain 150 mcg or more of iodine, and patients with hyperthyroidism should avoid iodine-containing supplements 2
• Cumulative effect: The combination of topical iodine and dietary/supplemental iodine creates additive exposure that can exceed the body's compensatory mechanisms 3

Immediate Evaluation Steps

The following diagnostic approach should be implemented:

• Measure serum TSH immediately; if TSH is <0.1 mIU/L, repeat within 4 weeks along with free T4 and total T3 or free T3 1
• For TSH between 0.1-0.45 mIU/L, repeat testing within 2 weeks given the acute iodine exposure and symptoms 1
• Consider 24-hour urinary iodine excretion to document excess iodine exposure 1
• Assess thyroid function comprehensively, as excess iodine can also cause hypothyroidism in some individuals 1

Management Recommendations

Immediate interventions include:

• Discontinue all iodine sources: Stop the topical 2% iodine applications immediately and discontinue the multivitamin (or switch to an iodine-free formulation) 2, 5
• Avoid additional iodine exposure: Eliminate iodized salt, seaweed/kelp products, excessive seafood, and iodine-containing supplements 2
• Symptomatic management: If hyperthyroid symptoms are significant (tachycardia, tremor, anxiety), beta-blockers can provide relief while awaiting iodine clearance 5, 7

Most cases of iodine-induced hyperthyroidism resolve spontaneously after iodine withdrawal, typically within weeks to months 5, 7. However, if hyperthyroidism persists or is severe:

• Antithyroid medications (methimazole or propylthiouracil) may be necessary 5, 7
• Radioactive iodine uptake and scan can help distinguish iodine-induced hyperthyroidism from other causes like Graves' disease 1

Important Caveats

Several clinical pitfalls warrant attention:

• Iodine-induced thyroid dysfunction can manifest as either hyperthyroidism OR hypothyroidism, depending on individual susceptibility 1, 4
• Patients with pre-existing nodular thyroid disease are at particularly high risk for developing overt hyperthyroidism with iodine exposure 1, 5
• The thyroid dysfunction is usually transient but can occasionally be prolonged or lead to permanent changes 4, 7
• Clinical signs of iodine toxicity may include metallic taste, gum and tooth soreness, abdominal pain, and gastrointestinal symptoms 1

Prognosis

The outlook is generally favorable with appropriate management. Iodine-induced hyperthyroidism typically abates after iodine withdrawal in patients with multinodular goiters or previously normal thyroid glands 5. The thyroid dysfunction is usually mild and transient, though monitoring should continue until thyroid function normalizes 6, 3. In rare cases where symptoms are severe or life-threatening, more aggressive intervention may be required 3.