Skin Mites Linked to Scabies, Rosacea, and Blepharitis
Skin Mite Problems
Skin mites are tiny creatures that live under our skin and in our hair follicles and oil glands. Scabies or itch mites tunnel into the skin and cause the disease known as scabies. Demodex mites infect the hair follicles or the oil glands next to the hair follicles. They may be harmless, but there is a growing suspicion that they are responsible for at least some cases of rosacea and blepharitis.
The main symptoms of scabies are an intense itch and the appearance of a red rash in the infected area. Rosacea is a condition in which the facial skin becomes chronically reddened. Blepharitis is an inflammation of the eyelid. Pinpointing mites as a cause of rosacea and blepharitis could pave the way for more effective treatments for the disorders, since some medications kill skin mites.
Anyone who suspects that they have scabies, rosacea, or blepharitis should visit a doctor for a diagnosis and treatment recommendations.
What Are Mites?
Mites are small creatures. Many are microscopic. They are members of the phylum Arthropoda and the class Arachnida, which is the class to which spiders belong. Mites and spiders are classified in different orders within the class Arachnida, however.
As in spiders, the body of a mite consists of a cephalothorax followed by an abdomen. In mites the two body sections are fused together and look like one structure, while in spiders the sections are connected by a stalk-like structure called a pedicel.
Like spiders, adult mites have a tough outer layer called an exoskeleton, or cuticle, as well as four pairs of legs. There are two pairs of appendages around the mouth—the chelicerae, or jaws, and the pedipalps, which are sensory structures.
Several mites attack the human body. Only the scabies and Demodex mites are referred to as "skin mites", however. They make their home in our skin, unlike other mites which attach to the skin temporarily.
Scabies or Itch Mites
The scabies mite, or Sarcoptes scabiei var. hominis, is a human parasite. The female mite has an oval shape and is about 0.4 mm long. Several long hairs extend from her body. Her legs are short and thick and she has no eyes. The male scabies mite is half the female's size.
The female burrows into human skin to lay her eggs, forming a tunnel just below the surface of the skin. As she digs, the mite feeds on cells and fluids released from damaged cells. Her body has short spines that help her attach to the wall of the skin tunnel.
A Living Scabies Mite
A person picks up scabies mites by prolonged and direct contact with the skin of an infected person. The mites can't jump or fly, so they must crawl from one host to another. Scabies mites may occasionally be transmitted by a contaminated object. They live for only 24 to 36 hours when they are outside the human body, however.
People of all socioeconomic backgrounds develop scabies. The infection isn't related to bad hygiene practices, so nobody should feel embarrassed about developing the disease.
What Does a Scabies Infection Look Like?
Life Cycle of the Itch Mite
Like other mites, the scabies or itch mite has four stages in its life cycle—the egg, the larva, one or more nymph stages, and the adult. The steps in the life cycle are as follows.
- The female mite deposits her eggs as she excavates her tunnel with her mouth parts and her front legs.
- The eggs hatch into larvae two to four days after being laid.
- Each larva travels to the surface of the skin and then creates its own burrow known as a molting pouch. Here the larva molts and goes through its nymphal stages before becoming an adult.
- A newly-formed adult male moves to the surface and enters a female's molting pouch, where he fertilizes her.
- Fertilized females travel over the surface of the skin until they find a new place to burrow or a new person to infect. A female can live for one to two months.
The scabies mite is also known as the itch mite because it causes severe itching. This itching is thought to be produced by an allergic reaction to the mite's eggs, feces, or saliva. The mite also produces a rash made of red pimples. Its tunnel sometimes forms a visible line on the skin.
Doctors can not only diagnose the presence of scabies but can also prescribe a medication to kill the mites that cause the disease. The medication is generally given in the form of a cream or lotion that is spread over the skin.
The Demodex mite is an elongated animal that has a worm-like body. It has eight, very short legs attached to the front of its body. Two species of Demodex may inhabit human skin. Demodex folliculorum lives in our hair follicles, including the ones that produce our eyelashes. This mite is up to 0.4 mm long. Demodex brevis lives in the sebaceous glands (or oil glands) that are located next to the hair follicles. It's only about 0.2 mm long. The mites are most common in facial skin but may be found on other areas of the body, too.
Unlike the scabies mite, Demodex forms a permanent relationship with humans that may not be harmful. It's often considered to be a normal inhabitant of our skin, just like the many bacteria that cover our body surface. In this case Demodex is involved in a commensal relationship with us instead of a parasitic one. In commensalism, one organism benefits from the relationship and the other is unaffected.
Demodex folliculorum Inside a Hair Follicle
Many researchers say that between 20% to 80% of us have Demodex mites in our skin. The percentage depends on the population that's tested and is highest in elderly people. Some researchers say that 100% of people over the age of ninety are infected by the mites.
Demodex Life Cycle
Demodex mites are transmitted from person to person by skin contact. Like scabies mites, Demodex mites crawl but can't jump or fly. They feed on cells within a hair follicle or on oil within a sebaceous gland.
The life cycle of Demodex folliculorum takes around 18 to 24 days to complete. The male and female mites emerge from their burrows at night and mate on the surface of the skin. They avoid exposure to light. After mating, the female returns to a follicle and lays 20 to 25 eggs. The eggs, larvae, nymphs, and new adults develop inside the follicle.
Photos and Videos of Demodex folliculorum
In some animals the number of Demodex mites greatly increases under certain circumstances and the mite becomes a parasite. For example, Demodex canis is a normal inhabitant of dog hair follicles. As in our body, Demodex mites in dogs generally cause no problems. The mite population sometimes grows out of control and causes a skin disorder called canine demodicosis, demodectic mange, or red mange, however. In this disorder, hair is lost from the skin and the dog develops bald patches.
Demodex may become a problem in dogs when the animal's immune system isn't working properly, when the dog is experiencing malnutrition, or when it's subjected to stress of some kind. There are treatments for the condition. While symptoms of demodectic mange are generally restricted to the skin, they may spread beyond the skin. Very occasionally, they may be life-threatening.
Demodex numbers sometimes increase in humans, too. The increase has been implicated in a variety of disorders, but researchers haven't yet proved that the mites can cause disease in humans. There is a possibility that they can trigger rosacea and blepharitis.
A Living Demodex Mite From a Dog
Rosacea is a disorder in which redness develops on the cheeks, nose, forehead, and/or chin. Blood vessels may be visible in the reddened area. Red pimples or bumps may be present as well. Someone with rosacea may also have dry skin that is easily irritated and a burning sensation in their eyes.
In severe cases of the disease, the nose may enlarge and become bulbous and red. This condition is called rhinophyma. W.C. Fields, a U.S. actor and comedian, is a famous example of a person who suffered from rosacea with rhinophyma. Fields died in 1946. Today surgery can remove the excess tissue from the nose.
The cause of rosacea isn't known for certain, which is frustrating for patients. There may be more than one cause of the disease. The disorder can be both uncomfortable and embarrassing. Some patients discover that certain factors make their rosacea worse. These factors include sun exposure, alcohol intake, and prolonged stress. Avoiding these triggers may improve the condition of the skin. Medications prescribed by a doctor may also help.
According to the NIH or National Institues of Health, rosacea is most common in women (especially during menopause), people between the ages of 30 and 60, and those with fair skin.
An Eye Doctor Discusses Rosacea and Associated Blepharitis
Blepharitis is an inflammation of the eyelids. The name of the disorder is derived from "blepharon", the Ancient Greek word for eyelid, and "itis", a suffix which means inflammation.
In blepharitis, the eyelids become red and itchy and may also become swollen, scaly, or crusty. Sufferers may find that their eyelids are sticky and that it's hard to open their eyes when they wake after sleeping. If a crust forms and enters the eyes, the eyes may feel gritty. Most symptoms develop next to the eyelashes.
Blepharitis is a common disorder. There are several factors which have been linked to the disorder, including a malfunctioning of the oil glands in the eyelids, the presence of bacteria, the existence of rosacea, and an allergic reaction.
Blepharitis and Its Treatment
Can Demodex Mites Cause Rosacea and Blepharitis?
Researchers have noticed that the number of Demodex mites is significantly increased in at least some cases of rosacea and blepharitis. There's a saying in biology that "correlation is not causation", however. We can't be certain that the increase in the number of mites is causing either rosacea or blepharitis. Instead, the two disorders may be producing conditions that favor an increase in the mite population. The rise in mite numbers may be a consequence of the disorders instead of the cause.
Nevertheless, researchers in the skin disease area are excited by the possibility that mites can cause rosacea and blepharitis and think that this relationship is a distinct possibility. Some clinicians are already finding that in certain cases giving patients medications that kill mites relieves them of their skin problem.
Some researchers use the term "Demodex dermatitis" to refer to a rosacea-like condition thought to be caused by mites. These researchers distinguish the redness caused by mites from the rosacea resulting from other causes.
Skin Mite Feces and Rosacea
Researchers at the Bayer College of Medicine in Houston, Texas, say that they have found bacteria in Demodex feces that trigger an immune reaction in humans. According to the researchers, this immune reaction is responsible for the inflammation and discomfort in at least some cases of rosacea.
Rosacea flares up under certain conditions, such as after sun exposure or exposure to humid conditions. The researchers suggest that this happens because the conditions promote mite activity.
Antibiotics are sometimes used to treat rosacea because they can reduce inflammation. Interestingly, corticosteroids, which also reduce inflammation, don't appear to help the disorder. The Bayer College scientists say that the antibiotics may work because they kill bacteria deposited by skin mites.
Other researchers have also suggested that bacteria from Demodex can have ill effects. They say these bacteria may enter our body from mite secretions or feces or from the decomposing bodies of dead mites.
An Eye Doctor Discusses Demodex and Blepharitis
Demodex and Human Disease
Scientists know that Demodex mites live in human skin, including the skin at the base of the eyelashes. They also know that the number of mites increases under certain conditions.
An increase in the Demodex population causes disease in other mammals, such as dogs. It therefore seems possible that the mites might cause disease in humans, too. This won't be known for certain until more research is done, though. Hopefully the situation will be clarified soon. If researchers discover that the mites can cause human diseases, they may then be able to find new and perhaps better treatments for these diseases. Fortunately, doctors already have ways to help people with rosacea or blepharitis as well as people with scabies.
Questions & Answers
© 2013 Linda Crampton