Testing

The Iodine Patch Test

A popular but unreliable way to check iodine status. Here's what it tells us and what it doesn't.

How It Works

Paint a 2-inch square of iodine (usually Lugol's) on the inner forearm. The idea is that if the stain disappears quickly (within a few hours), the body is deficient and "soaking up" the iodine. If it lingers, sufficiency is supposedly indicated.

Paint a patch

Apply 2-3 drops of Lugol's on the inner forearm in a small square.

Wait and observe

Note how long the orange-brown stain remains visible on the skin.

Interpret (loosely)

Fast disappearance suggests higher absorption; slow disappearance suggests lower absorption.

Why It's Unreliable

The disappearance rate depends on many factors beyond iodine status: skin thickness, temperature, humidity, blood flow to the area, and even clothing friction. The iodine also evaporates. It doesn't all get absorbed. This makes the test too variable to draw medical conclusions from.

Better Testing Options

The 24-hour urine loading test is considered more reliable for assessing iodine status. It measures how much iodine the body retains vs. excretes after a measured dose.

It's Still Useful for Something

While it can't diagnose deficiency, the patch test is a gentle way to start transdermal iodine supplementation. Painting a small amount on the skin is a very low-dose introduction that allows observing the body's initial response before taking iodine orally.