Iodide Ion (I⁻) Analysis · Iodine Spring Effects & Warnings

Table of Contents

What is Iodide ion?
Main Effects
Iodide ion Top 5 Hot Springs

What is Iodide ion?

Iodide ion (I⁻) at ≥ 10 mg/kg classifies the spring as an "iodine spring." Common in non-volcanic springs, it is said to have antibacterial action, and high cholesterol is listed as a drinking indication.

Main Effects

Indicated for high cholesterol (drinking)
Caution advised for hyperthyroidismIodine is a primary component used to produce thyroid hormones. For individuals with hyperthyroidism, such as Graves' disease, increased iodine intake can overstimulate the thyroid and may worsen symptoms. It is important to consult a physician before use.
Characteristic yellow-brown tint on air exposureThe water is initially clear as it contains colorless iodide ions (I⁻). Upon exposure to the air, these ions undergo oxidation and transform into iodine molecules (I₂). This chemical change is what gives the water its distinctive yellow-brown color.

Iodide ion Top 5 Hot Springs

Top 5 hot springs registered on this site with the highest content.

RANKING BY THIS MINERAL CONTENT

Choose a ryokan by how you bathe

Ryokan with private onsen

Plan your onsen trip

Onsen towns are often rural with patchy Wi-Fi and limited public transport. Sort out data, tours and a car before you go.

Includes affiliate links

References

SPRING TYPEMay 5, 2026· 1min read

Iodine-Containing Springs: A Non-Volcanic Rarity & Its Drinking Indication

Iodine-containing springs hold iodide ions (I⁻) at 10 mg/kg or more, mainly found in non-volcanic geological strata. Clear at first, they turn yellow when left to stand. Drinking is indicated for dyslipidemia. Note: persons with hyperthyroidism should be cautious.

MINERALMay 5, 2026· 1min read

Bromide ion: Main Effects & Top 5

Bromide ion (Br⁻) is found alongside chloride in sea-derived springs. It is said to be absorbed through the skin and calm nervous tension.

MINERALMay 5, 2026· 2min read

Metasilicic Acid: The "Beauty Spring" Standard Mineral & Top 5 Onsen

Metasilicic acid (H₂SiO₃) is a natural moisturizer also found in skincare lotions. Hot springs containing more than 50mg/kg are called "beauty springs" — leaving skin hydrated long after bathing. This is one of the therapeutic spring criteria in Japan's Mineral Spring Analysis Guideline (Table 1-1).

Iodide ion: Main Effects & Top 5