I remember, with some degree of horror, being handed a rubber model of a Demodex folliculorum, which, being several hundred times larger than the real thing, made it yet more shocking when I was told that it was more than likely that I had lots of these living in my face.

Humans can carry two follicular mite species: Demodex folliculorum, which live in groups in the infundibular portion of hair follicles, and Demodex brevis, which is a solitary species inhabiting the sebaceous glands of the skin. The mites are most numerous in the wings of the nose, on the forehead, in the ear canal, and (rather startlingly) on the nipples. Indeed, mite transmission is thought to involve transfer during breastfeeding. Hence, a prevalence of 90%, comparable with that of Herpes simplex virus, which is transferred by well-meaning but cold-sore carrying relatives.

Despite their somewhat gross appearance, the folliculorum species rarely causes problems. Hence, it is only in the past decade that ECPs have been made aware of the importance of Demodex as a possible cause of chronic and non-responsive blepharitis (see Optician 05.09.14 for our first review). It seems that demodicosis, the name given to the condition arising from an immune response to the mite, occurs when there is a mutation in the host immune system.

It is this that is the focus of a new paper,1 which hypothesises that the phasing out of the immune response is evidence that the mite is actually undergoing a change from a parasite to ‘an obligate ectosymbiont,’ one able to live ‘in harmony’ with its host. This change in life cycle is borne out by alterations in the mite that make it increasingly capable of life in our skin without causing any immune response.

Don’t throw away your tea tree oil wipes just yet; but maybe one day soon.

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References

1 https://doi.org/10.1093/molbev/msac125