What are chiggers?

Chiggers are the juvenile form (larvae) of a certain type of mite of the family Trombiculidae. Mites are arachnids (like spiders and ticks).

Chiggers are found throughout the world. They most commonly live in forests, grassy fields, gardens, parks, and in moist areas around lakes or rivers. Most of the larvae that cause chigger bites are found on plants that are relatively close to the ground surface, because they require a high level of humidity for survival.

What do chiggers look like?

Chiggers are barely visible to the naked eye (their length is less than 1/150th of an inch). They are red in color and may be best appreciated when clustered in groups on the skin. The juvenile forms have six legs, although the (harmless) adult mites have eight legs.

Picture of Chigger Eggs, Larvae, Nymph, and Adult

How do chiggers bite humans?

Chigger mites infest human skin via areas of contact with vegetation, such as pant cuffs or shirt sleeves and collars. They migrate on the skin in search of an optimal feeding area. A common myth about chiggers is that they burrow into and remain inside the skin. This is not true. Chiggers insert their feeding structures into the skin and inject enzymes that cause destruction of host tissue. Hardening of the surrounding skin results in the formation of a feeding tube called a stylostome. Chigger larvae then feed upon the destroyed tissue. If they are not disturbed (which is rarely the case because of they cause substantial itching) they may feed through the stylostome for a few days.

The chigger's mouth and feeding structures are delicate and are best able to penetrate the skin at areas of wrinkles, folds, or other areas of skin that are thin. Most bites occur around the ankles, the crotch and groin areas, behind the knees, and in the armpits. Barriers to migration on the skin such as belts may be one reason that chigger bites also commonly occur at the waist or at other areas where their migration is prevented by compression from clothing.

What are the symptoms of chigger bites?

A chigger bite itself is not noticeable. After the chigger has begun to inject digestive enzymes into the skin (usually after about 1-3 hours), symptoms typically begin.

• Pronounced itching is the most common symptom.
  
  
• The area of the bite may be reddened, flat, or raised; sometimes it resembles a pustule or blister.
  
  
• The itch is due to the presence of the stylostome and usually is most intense within 1-2 days after the bite.
  
  
• The itching persists for several days, and complete resolution of the skin lesions can take up to two weeks.

What is the treatment for chigger bites?

Many home remedies for chigger bites are based upon the incorrect belief that chiggers burrow into and remain in the skin. Nail polish, alcohol, and bleach have been applied to the bites to attempt to "suffocate" or kill the chiggers. But because the chiggers are not present in the skin, these methods are not effective.

Treatment for chigger bites is directed toward relieving the itching and inflammation. Calamine lotion and corticosteroid creams may be used to control itching. Oral antihistamines, such as diphenhydramine (Benadryl), may also be used for symptom relief.

What are complications of chigger bites?

Chigger bites themselves do not produce any long-term complications. However, because of the intense itching, prolonged scratching may lead to skin wounds that may become infected by bacteria.

How can chigger bites be prevented?

Washing with soap and water after outdoor activity may remove any chiggers that may be migrating on the skin and prevent their bites. Likewise, washing clothing that was worn outdoors will kill any chiggers remaining on the clothing.

Attention to the outdoor temperature can help with prevention of chigger bites. Chiggers do not bite at colder temperatures (below 60 F or 15.5 C). Chiggers also are not found in areas hotter than 99 F or 37.2 C, so hot rocky areas on sunny days can provide chigger-free seats.

As with mosquito bites, proper outdoor clothing can help prevent chigger bites. Long pants and long-sleeved shirts as well as thick socks and high shoes or boots can help prevent infestation. Pants legs should be tucked into shoes or boots if possible.

All mosquito repellents (such as DEET), applied to skin and clothing, are effective at repelling chiggers.

Chiggers At A Glance

• Chiggers are the larval (juvenile) form of a type of mite (Trombiculidae).
  
  
• Chiggers do not burrow into and remain inside the skin, contrary to popular belief.
  
  
• Chiggers inject digestive enzymes into the skin and feed upon the decomposed tissue.
  
  
• Pronounced itching is the main symptom of chigger bites.
  
  
• Bites may appear as blisters or as flat or raised red areas.
  
  
• Treatment involves supportive measures to control itching.

Reference:

Missouri Department of Conservation Web site, "Chiggers", http://mdc.mo.gov/nathis/arthopo/chiggers/, accessed 6/9/09.

sourceLast Editorial Review: 6/10/2009

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