How Flickering Lights can Cause an Allergic (MCAS) Response

Russell Irvin Johnston
3 min readMar 9, 2019


March 9, 2019
by Russell Johnston

Some LEDs, florescent lights, streetlights, and many other lights strobe at around 30 times per second (30 Hertz.) Sometimes, as little as 20 times per second. Others, at 60 Hertz. You may not consciously notice a strobe or flicker at 30 Hz, but then again you may. (Flicker fusion varies from person to person and time to time.) But your brain absolutely does notice it.

Speculation: I now think our brain/body mistakes all this flickering for nystagmus, a common symptom of poisoning or neurological damage. Therefore, it mounts a large non-IgE “allergic” response to cope with the poisoning that the body/brain imagines is happening. But nothing’s happening. Many of the odd symptoms of MCAS — such as having a severe reacting to a mere smell — happen because it’s so necessary for our body’s poison control mechanism to be preemptive; to mount a strong defense against a poison even before it enters the body, if at all possible; since poisons can kill.

It’s very common for those with Mast Cell Activation Syndrome (MCAS) to react badly to flickering lights or computer monitors (that strobe in many ways, not just the reported frame rate) if they use them for any length of time. It’s often assumed that the problem is EMF (electromagnetic fields), but finding strong evidence of that is difficult. Instead, I think the biggest problem with computer screens is simulated nystagmus, not EMF. Better implementations of that technology — monitors and operating systems that behaved differently, would certainly help with that, but don’t hold your breath.

Back to what we know:

Shown in the photo is something like a time lapse photograph of street lights as you go down the road in Tokyo. Not the best illustration for my purposes, but the best I can find. If you very quickly flick your eyes past a streetlight at night, or another strobing light: instead of a solid streak of light across your eyeball, you’ll see dots or dashes of light — because the light is turning off and on very rapidly. With a handheld light, such as an LED flashlight, you can move the bright end up and down very rapidly, and see either a solid streak, or a line of dashes.

With LEDs, the flicker often exists merely as a way to make the light less bright! One of my flashlights has two modes. Set to maximum brightness, there’s no flashing — just solid light that’s very bright. Set to normal brightness, it flickers at maybe 40 Hz, but with quite short dashes — the light is actually off most of the time.

Back to speculation again:

Why bother to do this to find out if a light is flickering when you can’t usually see the flickering? Again, your brain does notice and is monitoring for such symptoms in order to mount poison responses if it thinks they’re necessary. So a very unpleasant allergic response, or perhaps slowly increasing autoinflammation over weeks or months, can be triggered by that inconstant light; even though you can’t consciously see the flickering.

We’ve experienced an explosion in chronic illnesses of autoinflammation over the last fifty years, from heart disease, through diabetes, eczema, and endless more illnesses. I think flickering lights that mimic nystagmus are one of the reasons for that.

Below is a link to the Wikipedia page for nystagmaus, BUT! Warning — a .gif at the top of the page showing the eye flickering back due to nystagmus is itself going to be triggering for those bothered by flicker. Which is at least some evidence of the close relationship between the two phenomenon.

Previous health article in this series:
When a Cough or Bronchitis or Asthma won’t go away, and Antibiotics are no help: eosinophilic conditions

Full list of my health articles:



Russell Irvin Johnston

I've read at least the abstracts of (far) more than 250,000 peer-reviewed medical articles, I studied the history and philosophy of science at University.