The human hair follicle can become infected with bacteria and fungi, but many people do not know that these tiny hair-producing organs can also become infested with insects. The demodex mite is one such insect that can infest the hair follicles. Most people carry a few of these mites without experiencing any problems. However, in some instances these mite infestations can cause severe symptoms. Demodex mite infestations tend to affect the eyelids and eyes more than other areas of the body. It is easily treated but can be a serious problem for people living with HIV or suffering with other causes of a weakened immune system.
What is demodex?
Demodex is a group of mites that can infest human hair follicles. There are two main species of the Demodex mites that can infest human follicles. One only consumes the epithelial cells in the follicle, while the other consumes glandular cells in the adjacent sebaceous gland. Demodetic mites are similar to scabies and chiggers mites that also infest human skin. They are tiny and not visible to the naked eye. It moves very slowly by crawling from one site to another. The main food source of these mites is human skin cells and it does not feed on blood like other parasitic insects.
Infestation with Demodex mites is known as demodicosis. These tiny 8 legged mites are believed to be present on as many as 80% of the population. However, it does not pose a problem to the majority of people as its population size on the body is limited. Demodicosis mainly occurs in adults and older children. It is rarely seen in children younger than 5 years of age. People with a weakened immune system are at a greater risk, as the mites can proliferate rapidly and cause a more severe of demodicosis.
Types of Demodex Mites
The two species of human demodetic mites is Demodex folliculorum and Demodex brevis. These mites tend to have a predilection for the follicles of the eyelids and surrounding region. Demodex folliculorum mites are about 0.3 to 0.4mm in length, which is twice the size of Demodex brevis (around 0.15 to 0.20mm in length). Demodex canis is the demodetic mite that infests dogs but it can occasionally cause an infestation in humans.
- Demodex folliculorum mites feed on the epithelial cells of the hair follicle. It causes the follicle to distend and thicken. This also contributes to the formation of keratin (skin protein) plugs. These mites may reside in follicles anywhere on the body but tend to prefer the hair follicles of the face.
- Demodex brevis mites feed on the glandular cells of the sebaceous gland that attaches to hair follicles (pilosebaceous glands) and meibomian glands. The sebaceous glands produce an oily substance known as sebum. Meibomian glands produce meibum which prevents tears from rapidly evaporating. It plays an important role in eye moisture.
The mites spend their entire life on the human body although it can fall off and live on inanimate objects for a short while before infesting a person. It tends to move around in the dark but hides away in the follicles in daylight. The female mites have a tendency to remain in one follicle where they mate and lay eggs. The male mite travels around from one follicle to another where they mate with female mites.
Demodex Infestation Symptoms
Demodex infestations affect the hair follicle and attached glands, especially of the eyelids. The symptoms of Demodex infestation are therefore seen mainly on the eyelids. However, this only occurs when the mite population increases significantly and when it cause sufficient irritation and damage to the area. A few mites in an otherwise healthy person may not lead to any symptoms.
Eye and Eyelid Symptoms
The symptoms of demodicosis include:
- Thickening of the eyelids
- Scaling of skin on the eyelids
- Itchy eyelids
- Loss of eyelashes (madarosis)
- Decreased vision
- Dry eyes
Demodicosis could possibly play some role in blepharitis, which is inflammation of the eyelids. It may also lead to bacterial infections of the conjunctiva and cornea.
Demodex are not known to conclusively cause any skin diseases. However, large numbers of mites have been found in people with some of the skin conditions below. It is therefore believed that it could possibly play some role in the causation of these skin diseases which predominantly occur on the face.
- Pityriasis folliculorum where the skin becomes rough, dry and scaly.
- Rosacea which is marked by patches and plaques of intensely red skin.
- Perioral dermatitis where there is itching, dryness and roughness of the skin around the mouth.
In most cases demodicosis does not require treatment with prescription medication. It can be managed at home with simple conservative measures. However, given that it can lead to serious symptoms like diminished vision, demodicosis treatment should be overlooked by a medical practitioner. Bacterial infection of the conjunctiva and cornea requires prompt medical treatment.
- Wash the hair and eyelashes with shampoo daily.
- Exfoliate the dead skin cells every now and then.
- Cleanse the face with an appropriate cleanser at least twice daily.
- Oily makeup and facial creams should be avoided. Old makeup should be discarded.
- Tea tree face washes or soaps may be helpful.
- Bed linen (sheets and pillow cases) should be changed frequently and washed thoroughly.
- Scrubs are used to debride the lashes and roots.
- A combination of tea tree oil and Macadamia nut oil are applied to destroy eggs.
Although this treatment uses non-prescription herbal remedies, it should only be done by a doctor. Other applications that may be used includes mercury oxide ointment and rubbing alcohol.
- Tea tree 5% ointment.
- Mercury oxide 1% ointment.
- Topical insecticides like permethrin and crotamiton creams.
- Topical antibiotics like erythromycin and metronidazole.
- Oral medication like ivermectin for people with weakened immune systems such as in HIV infection.
Eradication and Recurrence
The recovery from demodicosis is very good. The mite is almost never eradicated entirely from the human body. However, when the mite population is significantly reduced then it no longer tends to cause a problem. This has to be maintained with proper hygiene on an ongoing basis or a recurrence is very likely to occur. The condition is still easily treated if it recurs.