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SEM image of the week: Never put anything smaller than your elbow in your ear

Posted on Monday, November 21, 2011 by for SEM.

The subtitle of this week’s post comes from an oft-quoted aphorism in the medical world. "Never put anything smaller than your elbow into your ear." Given that your elbow is much thicker than your ear canal, and given that you couldn’t possibly contort your arm enough to point your elbow toward your head, medical professionals are basically telling us not to put anything into our ear canal under any circumstance.

On the surface, cotton swab manufacturers seem to agree with this given that their products come with warnings that read something like this …

Do not insert swab into ear canal. Entering the ear canal could cause injury.

Why then are cotton swabs made smaller than the ear canal? This is not a question we feel qualified to answer here at Midwood Science. Our primary question is always, "What do things look like?" Bigger may be safer, but smaller is more interesting. Now that we have a scanning electron microscope (SEM), small is our favorite size.

Cotton doesn’t conduct electricity very well, so charge from the electron beam piles up over time instead of flowing away. At low magnifications, this build up of charge deflects a significant portion of the beam towards the detector, which makes the image look "hot". At high magnifications, surface charges deflect the beam unpredictably, which results in a sort of "underwater" appearance. Despite the distortion, we all know what we’re looking at. The images below are what a typical cotton swab looks like under an SEM.

The head of the cotton swab. The neck of the cotton swab, where the fuffy cotton head joins the matted paper stalk.
A pile of fibers under high magnification … … looks like a mangrove swamp under very high magnification.

Image credit: Glenn Elert.