What are Demodex mites?
Demodex is the genus of certain types of mites that can infect the hair follicles in humans. Unlike other parasitic mites, Demodex mites do not feed on human blood. They derive their nutrition by feeding on human skin cells. There are two main species of the Demodex genus that commonly affect humans. One species of Demodex feeds on the glandular cells of the sebaceous glands associated with the hair follicles.
The other species of Demodex feeds on the epithelial cells that line the hair follicles. Demodex mites usually crawl slowly from one follicle to another on the surface of the skin. These mites are very small in size. Therefore, they are invisible to the naked eye. Demodex mites have eight legs, and are similar to the mites that cause chiggers and scabies. All of these mites can infest human skin and cause a skin rash.
Read more on skin mites.
Demodex Mite Infestation
The technical term for infestation with Demodex mites is demodicosis. It is believed that around 80% of the human population is infested with Demodex mites. However, most people are unaware of the infestation because these mites do not cause noticeable symptoms when they are present in small numbers. In some cases, the population of Demodex mites may become large enough to cause severe symptoms.
Demodicosis is rarely seen in children below the age of five years. Most of the affected individuals are older children and adults. Demodicosis can cause severe symptoms in individuals who have a weakened immune system (such as people suffering from AIDS). The weak immune system in such individuals allows rapid growth of the Demodex mite population, resulting in a severe form of demodicosis.
Although hair follicles are present all over the body, the Demodex mites are most commonly found in the hair follicles that are located on the eyelids. The hair follicles in other parts of the body are not as frequently affected as those present around the eyes. Demodicosis can be treated easily. However, this condition could be a serious problem in individuals with a weak immune system.
Types of Demodex Mites
As mentioned previously, human hair follicles predominantly get infected by two different species of Demodex mites. These two species are Demodex brevis and Demodex folliculorum. Both these species of Demodex mites have a predilection for the hair follicles on the face and eyelids.
Demodex folliculorum, as the name suggests, infest the hair follicles and feed on the epithelial cells of the hair follicle. The mites of this species can growth up to 0.3-0.4 mm in length. Infestation of the hair follicles with Demodex folliculorum results in thickening and distension of the follicles. This distension of hair follicles facilitates the formation of keratin plugs. Demodex folliculorum commonly affects the hair follicles on the face. However, these mites can also infest hair follicles that are present elsewhere on the body.
Demodex brevis also infests the hair follicles, but feeds off the glandular cells present in the glands that are associated with the hair follicles. These glands include the sebaceous glands that produce an oily substance known as the sebum, and the meibomian glands that produce a substance called meibum.
Meibum plays a key role in maintaining the moisture in the eyes by preventing rapid evaporation of the tears. Mites belonging to the Demodex brevis species are smaller than the mites that belong to the Demodex folliculorum species. Mites of the Demodex brevis species can grow up to 0.15-0.20 mm in length.
Apart from the above two species of Demodex mites, human hair follicles can also get infested with Demodex canis species. Demodex canis typically causes infestation of the hair follicles in dogs. Humans get affected by this species only occasionally.
Where do Demodex mites live?
Even though the parasitic Demodex mites spend most of their lives clinging to the human body, they are also capable of surviving on inanimate objects for a short time. When a person comes in contact with such an inanimate object, the mites attach to the skin and reach the hair follicles.
Demodex mites typically move when it is dark. They hide in the hair follicles during day time. It is usually the male mite that moves from one follicle to another, while the female mite remains in one follicle. Male mites travel between follicles to mate with the female mites.
Signs and Symptoms
The majority of individuals who carry the Demodex mites on their body do not show any symptoms. The symptoms occur only when the mite infestation becomes severe due to rapid growth of the mite population. Symptoms of Demodex mite infestation usually involve the areas around the eyes. Some symptoms also arise in the skin.
Eyes and eyelids
Demodex mite infestation in the hair follicles around the eye region causes symptoms that include itching of the eyelids, dryness of the eyes, loss of eyelashes, thickening of the eyelids, conjunctivitis, scaly skin on the eyelids, and visual problems. Inflammation of the eyelids (blepharitis) may also occur due to Demodex mite infestation. Such inflammatory reactions could also lead to secondary bacterial infections of the cornea and conjunctiva.
There is no conclusive evidence that Demodex mites cause skin diseases. However, Demodex mite infestations have been seen to occur alongside some skin conditions, such as rosacea, pityriasis folliculorum, and perioral dermatitis. These skin conditions usually affect the face. Therefore, it is believed that Demodex mite infestation may have some role to play in these skin conditions.
Read more on rosacea.
Treatment of Demodex Mite Infestation
Demodex mite infestation can be treated easily at home using some simple remedies. Prescription medications are not required in most cases. However, proper medical treatment should be sought if symptoms become severe. For example, prompt medical treatment is warranted when visual disturbances and bacterial infection of the eyes occur.
Simple home remedies to treat Demodex mite infestation include washing the eyelashes and hair daily with a shampoo, using a cleanser to cleanse face regularly, exfoliating dead skin on the face, and avoiding greasy facial creams. One should also change and wash the bedding material frequently.
Medical treatment of Demodex mite infestation includes using 1% mercury oxide ointments, antibiotics such as metronidazole and erythromycin, insecticide creams containing crotamiton and permethrin, and oral ivermectin. Scrubbing of eyelashes and application of a mixture of macadamia nut oil and tea tree oil may also be done by the doctor in order to destroy mite eggs.
Even though Demodex mites do not get eradicated completely, the population of the mites decreases significantly with treatment. This is enough for the symptoms to disappear. After treatment, one should continue to maintain proper hygiene in order to prevent a recurrence of the symptoms.