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8 November 2022

Blepharitis and the mites that live on your eyelids

Demodex mite

This article was written by Liz Ball and David Lunt, and originally published in Insight magazine

“There are mites living on your face, they can poop and cause conditions like blepharitis”, or so recent media reports claim. It’s a bit of a revolting thought, especially considering that mites are related to spiders. But is it true? To find the facts, Liz Ball, Glaucoma UK’s Development Manager for northern England, spoke to David Lunt, a Consultant Ophthalmologist at South Tees Hospitals NHS Trust.

Are there really mites living on our faces and do they cause blepharitis?

Tiny organisms, like bacteria and mites, are constantly moving in, out, through and around our bodies. Most of the tiny organisms living in and on us get on with their business without ever bothering us. We even rely on some of them to keep us healthy, like the good bacteria in our guts. Mites living on our skin help to keep it clean. But, if their population gets too dense or unbalanced, they can start to cause us harm. It’s thought that large or unbalanced populations of mites around the eyelids might cause blepharitis in some people. But there are lots of other causes of blepharitis, too.

What are the mites living on our eyelids?

Two types of mites, ‘Demodex folliculorum’ and ‘Demodex brevis’, commonly live around our eyelids and eyelashes. They’re often referred to together simply as Demodex mites. Demodex mites are so common that everyone over the age of 75 is thought to have them. They are tiny, cigar-shaped arachnoids, related to spiders, measuring up to 0.4mm. In small numbers, they might help to keep our eyelashes clean.

How might mites cause blepharitis?

Given that Demodex mites are so common, their role in blepharitis is not fully understood. However, it’s thought that they might contribute to blepharitis in some people in a few different ways:

  • Firstly, the mites feed on the cells in the follicles at the base of our eyelashes and in the meibomian glands. Their biting, and the enzymes they use to digest their food, cause irritation.
  • Secondly, Demodex mites deposit undigested food, their eggs and their dying bodies in the follicles and glands. Their live bodies can attract other debris, like our cells or the oil made by the meibomian glands, and create a blockage in the glands.
  • Thirdly, Demodex mites carry bacteria, like ‘Staphylococcus aureus’, that can trigger inflammation that leads to blepharitis. Demodex mites are a normal part of our bodies’ ecology, but it’s possible that when there are too many of them, over time, they can trigger blepharitis.

What about treatment for blepharitis caused by Demodex mites?

It’s thought that tea tree oil might slow or prevent Demodex mite reproduction. Therefore, wiping eyelids with a weak solution of tea tree oil might help. However, it’s unclear how effective this is.

There are lots of possible causes of blepharitis. Most treatments for blepharitis are the same, whatever the cause. Find out more about the condition and how to manage it in our leaflet titled ‘Blepharitis’.

Why have Demodex mites been in the news recently?

Research published earlier this year found that ‘Demodex folliculorum’ mites are evolving to become increasingly dependent on us. For example, they’ve lost the genes that control their day-night cycle and instead rely on chemicals we produce to control it. Similarly, they’ve lost some genes related to reproduction. These changes mean that, over time, ‘Demodex folliculorum’ mites might become extinct.

Phew, fewer mites on our faces! Isn’t that a good thing?

Evolution happens slowly, so there’s little chance of ‘Demodex folliculorum’ mites becoming extinct yet. But, when they do die out, they’ll no longer help to clean our eyelashes for us. Plus, it will change the balance of tiny organisms living on our eyelids. At this time, we can’t be sure what that will mean.