Parasites have many effects on human skin. Known as organisms living on a host from which they take nourishment, parasites usually enter into, escape from or reside on skin. Mites and lice bite or burrow into skin, causing itching and irritation. Ticks inflict bite wounds and feed on blood, while spreading disease. Even fungus, also a parasite, causes skin damage, allowing secondary bacterial infections to occur. Many parasitic organisms change the condition of skin.
Pain
Parasites usually bite, burrow or chew on skin. Skin is made up of three layers that protect the body from environmental invasion. The outer layer of skin, the epidermis, does not have nerves. Just under the epidermis is the dermis. The dermis is supplied with nerves extending from the deepest fat layer, or hypodermis. If a parasite invades the skin layers deeply enough, nerve endings are activated and pain occurs. Some parasites, such as ticks, inject anesthetic-type compounds into the bite area, rendering the nerves inactive. Skin pain allows a person to react and rid the skin of the parasite; but if the parasite goes undetected, it can complete its life cycle.
Swelling and Itching
Usually the skin reacts to parasitic infestation with an inflammatory or allergic reaction. If the parasite is invasive, the skin becomes damaged and an inflammatory healing reaction occurs. Scabies mites burrow into the skin and lay eggs. When the eggs hatch, larvae travel to the skin's surface and cause severe itching. Parasitic skin itching is usually caused by the body's release of histamine in response to the anticoagulants injected into the skin by the parasite. Histamine causes the blood vessels and nerves to swell, leading to an itching sensation with swelling.
Blisters and Crusting
Many parasites cause skin to itch. Scratching causes increased friction on the skin and the inner layers of skin may separate from the outer layers. The space between the layers fills with lymph fluid as your body tries to heal the damaged skin. The lymph fluid causes blisters -- small fluid-filled bumps -- to form. As the blisters break open, the fluid is released and dries in the area around the skin lesion, which causes a dry crust to form. Fungal parasites cause blisters and crusting. Athlete's foot causes cracked skin and blisters.
Bacteria
Opportunistic bacteria cause secondary infections to parasite infestations. As the skin is damaged by the parasite or self-inflicted scratching, the bacteria invade the skin and work their way to a blood supply. When they reach the blood nutrients, they multiply dramatically and cause a secondary infection. Many times, treatments for parasites must include an antibiotic to combat a secondary bacterial infection.
Scarring
Skin parasites do not usually cause scar formation. Scarring occurs due to damage imposed on the skin by scratching. If untreated parasites, such as scabies mites, continue to multiply on the human body, the itching sensation becomes excessive and repeated scratching damages skin. As the skin wounds heal, fibrous tissue replaces normal skin, causing a scar. Scars can be dark or light and raised or pitted. Controlling the parasite eliminates secondary scarring.
