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Will Iodine on Nails Upset Thyroid Function?

Painting white iodine on nails is a popular remedy for nail fungus. Iodine can be absorbed through skin, but not much through nails.
Will Iodine on Nails Upset Thyroid Function?
Cracked fingernails with brittle splitting and peeling nails

Iodine is not a glamorous mineral, even though it is essential. Your body cannot make thyroid hormones without iodine. In addition, this mineral may also be critical for mounting a normal immune response. Normally, you get the iodine you need from using iodized salt in your food, drinking milk or eating seafood once in a while. In the US, average intake is comfortably within the healthy range, but getting too much iodine can be just as risky as consuming too little. That’s why one reader is worried about using iodine on nails to counteract nail fungus.

Can Iodine on Nails Be Absorbed?

Q. In a recent article, a person said that having a scan with iodine led to signs of hyperthyroidism. A thyroid doctor found antithyroid antibodies in the patient’s blood. You replied that some people react to iodine exposure by developing thyroid problems.

I have been considering using decolorized (white) iodine on my fingernails, which are weak and brittle. Painting iodine on nails every day for a week and then weekly after that is supposed to strengthen the nails.

Now I wonder if that is safe. Although my thyroid levels have always been normal, there are thyroid problems in my family (sibling, aunts and uncles are on Synthroid).

Using Decolorized Iodine to Fight Nail Fungus:

A. We have heard from a number of readers that decolorized iodine can be helpful against nail fungus. It does have antifungal activity. We do not know whether it could strengthen nails that are simply brittle but not infected. Occasionally, brittle nails signal an underactive thyroid gland, though. Consequently, if you have other symptoms (fatigue, constipation, dry skin, mental fogginess, hair loss), you should see your doctor.

It is unlikely that putting iodine on your nails will affect your thyroid gland. When povidone iodine is used as a disinfectant, the skin absorbs it and urinary excretion increases significantly (Thyroid, June 2005). This returns to normal within three to five days.

So far as we can tell, no one has measured iodine absorption through finger- or toenails. However, nails do not absorb minerals very well. As a result, these surfaces seem less likely to absorb large quantities of the mineral than skin. We would be very surprised if putting white iodine on nails led to enough iodine absorption to make a difference for thyroid function.

Even dietary iodine through multivitamin pills does not appear to increase the chance of thyroid cancer or other thyroid problems (Cancer Epidemiology, Biomarkers & Prevention, Sep. 2001). On the other hand, the dose of iodine used in contrast material during a medical scan is huge, more than 30 times the minimum daily allowance for this mineral (JAMA Otolaryngology-Head & Neck Surgery, May, 2013). 

To learn more about keeping nails healthy and fighting nail fungus, you may wish to read our free Guide to Hair and Nail Care. It can be found in the Health eGuides section. There, you will also find our eGuide to Thyroid Hormones, an online resource with a wealth of information on thyroid health.

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies. .
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  • Tomoda C et al, "Transcutaneous iodine absorption in adult patients with thyroid cancer disinfected with povidone-iodine at operation." Thyroid, June 2005. DOI: 10.1089/thy.2005.15.600
  • Horn-Ross PL et al, "Iodine and thyroid cancer risk among women in a multiethnic population: the Bay Area Thyroid Cancer Study." Cancer Epidemiology, Biomarkers & Prevention, Sep. 2001.
  • Nimmons GL et al, "Urinary iodine excretion after contrast computed tomography scan implications for radioactive iodine use." JAMA Otolaryngology-Head & Neck Surgery, May, 2013. doi:10.1001/jamaoto.2013.2552
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