Microscopic monsters are living on your body – these are the signs they’re causing trouble

Forget spiders, bats and other Hallowe’en creepy crawlies. Some of the more gruesome creatures are considerably closer to home: living in your eyelashes, feasting on the oil in your skin and setting up home between your toes.

Take Demodex, the microscopic mites that live in our hair follicles. A study last month examined eyelash samples from 25 young women who regularly wore eyelash extensions and found Demodex in 24 of them. Eighteen also showed signs of inflammation associated with the mites. An uncomfortable reminder, perhaps, that our bodies are crawling with microscopic life.

Yet before you begin washing out your eyes, most of it is supposed to be there.

“We’ve got about 20 billion bacteria on our skin,” says Prof Carsten Flohr, professor of dermatology at St John’s Institute of Dermatology, King’s College London and Guy’s and St Thomas’ NHS Foundation Trust. “They’re a really important part of an intact, healthy skin barrier. What you want is a diverse bacterial flora.”

Different organisms favour different parts of us, determined partly by factors such as skin pH, oiliness, moisture and temperature. What matters is not simply which bugs we carry, but how numerous they become and how our immune system reacts to them.

So which of our microscopic lodgers should we worry about, and which do we actually need?

Eyelashes

Demodex folliculorum lives naturally inside hair follicles, including those at the roots of our eyelashes. It is commonly found in healthy people and becomes more prevalent with age.

These mites are commonly found in healthy people, explains Su-yin Koay, a consultant ophthalmologist at Moorfields Eye Hospital. Problems only arise when numbers increase. “They can contribute to inflammation of the eyelid margins, known as Demodex blepharitis.

“Blepharitis can cause redness, itching, grittiness, crusting and recurrent eyelid lumps called chalazia. It can also disrupt the tear film, causing dry eyes and fluctuating vision.”

One tell-tale sign of Demodex blepharitis is “collarettes” or cylindrical dandruff: waxy deposits forming a sleeve around the base of the eyelashes.

“Eyelash extensions may make matters worse because wearers can be reluctant to clean thoroughly around them, allowing oil and debris to accumulate. Meanwhile, adhesives can also cause irritation or allergic reactions.”

How to treat it

Blepharitis is chronic but can usually be controlled with good daily eyelid hygiene. Koay recommends applying a warm compress or heated eye mask for five to 10 minutes, gently massaging the lids towards the lashes, then cleaning around the roots of the eyelashes to remove debris and excess oil. Seek advice for persistent irritation, redness or recurrent eyelid lumps.

Face

Demodex also inhabits facial hair follicles and sebaceous glands, feeding on sebum. Most of the time it causes no trouble.

“People with rosacea, however, often have higher numbers, particularly those with the red, bumpy papulopustular form.

“We do not think the mites are the sole cause of rosacea, but in high numbers they may contribute to inflammation,” says Dr Derrick Phillips, a consultant dermatologist.

The mites may physically irritate hair follicles, provoke an immune response and alter the balance of bacteria on the skin. This can create a cycle “where inflammation encourages greater mite proliferation, which in turn drives more inflammation”.

How to treat it

Topical ivermectin can be particularly useful for inflammatory rosacea associated with Demodex, says Dr Phillips. Other treatments include metronidazole, azelaic acid and, when necessary, oral antibiotics such as doxycycline. Persistent redness, burning or crops of red bumps and pustules warrant further assessment.

Armpits

It isn’t actually your sweat that smells.

“Fresh sweat is largely odourless,” says Dr Phillips. Body odour develops when bacteria living in our armpits, particularly Corynebacteria, break down components of sweat into volatile compounds.

How to treat it

Regular washing, deodorant and antiperspirant are usually sufficient, while excessive sweating can be treated as hyperhidrosis with stronger prescription-strength or aluminium chloride-based antiperspirants and gentle soap substitutes, or oral medications.

Occasionally, Corynebacterium minutissimum causes erythrasma: pink or brown, slightly scaly patches in areas such as the armpits or groin. Dr Phillips sees patients who mistake it for eczema or a fungal infection. Intriguingly, under UV light erythrasma typically fluoresces coral pink. It can usually be treated with topical, or occasionally oral, antibiotics.

Scalp

Malassezia is a family of yeasts naturally found on our skin, particularly in oily areas.

“They like the scalp, but Malassezia also likes the eyebrows and the nasolabial folds [often called smile or laughter lines],” says Prof Flohr. Why? The local “microclimate”, including skin pH and temperature, suits them.

In some people, Malassezia contributes to dandruff and seborrhoeic dermatitis, producing redness, itching and flaking.

How to treat it

Dr Phillips recommends starting with an antifungal shampoo containing ingredients such as ketoconazole or selenium sulphide. Significant inflammation may require a short course of topical steroid.

And beware of treating every flaky scalp with oil. “I see people treating persistent flaking as a dry scalp and adding more oils, when this can actually make seborrhoeic dermatitis worse,” he says. Seek advice if the scalp is painful, very inflamed, causing hair loss or fails to improve.

Feet

Warm, damp feet are the perfect breeding ground for fungi.

Prof Flohr compares our microbiome to different plants thriving in different gardens. “Certain plants only grow in certain front gardens because of the mixture of soil that plant needs.”

Athlete’s foot is caused by dermatophytes, fungi that infect skin, hair and nails. “These fungi thrive in warm, moist environments,” says Dr Phillips. Sweating, enclosed footwear and sitting in damp socks all increase the risk; infections can also be picked up in gyms and swimming pools.

Typical symptoms include itching, redness, peeling and cracking between the toes.

How to treat it

Most cases respond to a topical antifungal such as terbinafine, combined with keeping feet dry and promptly changing sweaty socks and footwear. Recurrent, painful or widespread infections, or those spreading to the toenails, should be checked. Dr Phillips also sees people who treat “athlete’s foot” for months when they actually have eczema or psoriasis.

And the bugs that help you…

Perhaps the biggest misconception about our skin bugs is that we would be healthier without them.

One of the “good guys”, as Prof Flohr calls it, is Staphylococcus epidermidis. Despite its alarming-sounding name, it forms part of the normal flora established soon after birth.

Dr Phillips says bacteria such as S. epidermidis work symbiotically with our skin cells, helping support the skin barrier, regulate immune responses and limit the growth of potentially harmful microbes.

Even Cutibacterium acnes – a name hardly conjuring up perfect skin – isn’t inherently bad. It is a normal resident of healthy skin; particular strains are more strongly associated with acne.

What matters is balance – and the condition of the skin underneath. Prof Flohr compares a healthy skin barrier to “a wall with bricks and mortar”. Eczema skin, by contrast, is “a bit like a desert, it’s cracked open”, giving harmful bacteria somewhere to gain a foothold.

One opportunist is Staphylococcus aureus, which can contribute to infected eczema and impetigo and produce toxins that provoke itching, swelling and redness.

“If you’ve got a strong wall, a strong barrier, bacterial infections rarely have a chance,” says Prof Flohr.

“So however tempting the Hallowe’en horror story of mites, fungi and billions of bacteria may be, the answer isn’t to scrub ourselves sterile. We are ecosystems as much as individuals – and most of our microscopic inhabitants aren’t invaders at all. They are simply part of being human.”

Try full access to The Telegraph free today. Unlock their award-winning website and essential news app, plus useful tools and expert guides for your money, health and holidays.