Skin is the largest organ in the human body. As the body's external barrier, skin comes into contact with a host of parasites that live on and thrive off of it. Some of these parasites are passed from person to person through touch, while others are opportunistic travelers that alight on any passing warm body. Regardless of mode of transmission, parasites run the gamut from the unnoticed to the mildly annoying to the life-threatening.
Bedbugs
Bedbugs are reddish-brown, wingless insects that feed primarily on humans. They are nocturnal and hide during the day in furniture, clothing, walls, between floorboards and in other crevices. While bedbugs have not been implicated in the transmission of disease, their bites can cause bedbug-dermatitis, a red, swollen eruption at the site of the bite. Eradication of bedbugs is extremely difficult.
Fleas
Flea bites are annoying not only because they itch, but because they can lead to secondary infection from scratching or even to death if the flea carries the bacterium that causes bubonic plague. Usually, infected fleas move from rodent to rodent. Occasionally, a flea will feed on an infected rodent and then pass to a human. Initial plague symptoms include fever and a feeling of general malaise. According to the Centers for Disease Control, these symptoms are followed by regionalized hot, painful swollen glands, called buboes.
Lice
Lice are insects that move by crawling from host to host. They do not hop or fly and, therefore, person-to-person contact is necessary for transmission. Human lice feed only on humans, so contact with pets or other animals is not a factor in their spread.
There are three types of human lice, and each feeds on a different part of the human body: head lice, body lice and "crabs," or pubic lice. Of the three, only body lice transmit disease. Trench fever, epidemic typhus and epidemic relapsing fever are transmitted by body lice.
Mites
Mites burrow under the top layers of skin to live, feed and lay eggs. The bites cause itching and small, pimple-like eruptions. Scabies is an infestation of the human itch mite. Transmission usually occurs after prolonged skin-to-skin contact and, in addition to the bite eruptions, burrow-trails can sometimes be seen on the skin of an infected person.
Crusted scabies, also called Norwegian scabies, is a severe mite infestation. People with crusted scabies are extremely contagious and transmission can occur through simply touching an item an infected person has touched.
Ticks
Unlike other parasites that feed on human skin, ticks are not generally particular about their food source. They will feed off any number of mammals and bird species and, because they travel with their host, disease can spread quickly.
Ticks transmit a number of diseases that are harmful to humans, including Lyme disease, Rocky Mountain spotted fever and southern tick-associated rash illness. A number of tick-borne diseases first present with a distinctive rash, accompanying headache and muscle ache, and sometimes fever. Some of these diseases can cause chronic illness.
