Chiggers are tiny, nearly invisible parasitic mites belonging to the family Trombiculidae, which are more closely related to spiders and ticks than to insects. The term “chigger” refers to the minute, six-legged larval stage of the mite, which is the only stage that feeds on humans and animals. These larvae measure less than 0.3 millimeters, making them difficult to spot with the naked eye. Although the bites are typically just an outdoor nuisance, they cause a condition known as trombiculiasis, characterized by intense itching and localized skin irritation.
The Biology and Typical Habitat
The chigger life cycle involves seven distinct stages, but only the larval form is parasitic. Larvae, which are often yellow, orange, or light red, have six legs, differentiating them from the eight-legged nymphs and adults. The post-larval stages are harmless to humans, living in the soil where they feed on small arthropods and insect eggs.
Chiggers thrive in environments that provide warmth and moisture, such as low-lying vegetation, wooded areas, and tall grasslands. They frequently wait on the tips of leaves and grass blades, a behavior called “questing,” where they await a passing host. Once a human or animal brushes past, the larvae quickly attach to the skin or clothing and begin to migrate in search of a suitable feeding site.
The Biting Mechanism and Symptom Development
A misconception is that chiggers burrow into the skin or suck blood, but they do neither. Instead, the larva uses specialized mouthparts called chelicerae to pierce the skin, injecting digestive enzymes from its saliva. These enzymes dissolve the host’s skin cells, liquefying the tissue around the feeding site.
The host’s immune response to this foreign enzyme causes the surrounding tissue to harden, forming a stylostome. The chigger uses this stylostome like a feeding tube to ingest the digested cellular fluid. This process is the source of the irritation and itching.
Itching often does not begin immediately but is typically delayed for several hours after the chigger has begun feeding or has already dropped off. The characteristic skin lesions are small, red, raised bumps, which may resemble pimples, blisters, or small hives. These welts commonly appear in clusters where clothing fits tightly, such as around the waistline, ankles, behind the knees, or in skin folds. The itching can persist for several days, and the lesions may take one to two weeks to fully resolve.
Immediate and Follow-Up Treatment
The first step after potential exposure is to take a hot, soapy shower or bath immediately to dislodge and wash away any attached larvae. Vigorously scrubbing the skin with a washcloth helps remove lingering mites. Promptly washing all exposed clothing in hot water and drying them on a high-heat setting will also kill any chiggers remaining on the fabric.
Once the larvae are removed, treatment focuses on reducing the inflammation and itching caused by the stylostome and the body’s reaction to the enzymes. Topical anti-itch remedies like calamine lotion, hydrocortisone creams, or topical anesthetics containing pramoxine can provide relief. Oral antihistamines can also help control the systemic allergic reaction and reduce nighttime itching.
Avoid scratching the bumps, as this can break the skin and introduce bacteria, potentially leading to a secondary infection like impetigo or cellulitis. If the lesions show signs of infection, such as increasing redness, warmth, swelling, or pus, or if symptoms fail to improve within two weeks, consult a healthcare professional.
Effective Prevention Strategies
Proactive measures are the most effective way to avoid chigger bites, particularly when spending time in areas known to harbor them. Chemical treatment of clothing with permethrin, an insecticide that kills chiggers upon contact, is recommended. Permethrin should be applied to clothing and gear, such as socks and pants, but not sprayed directly onto the skin.
Skin-based insect repellents containing DEET, picaridin, or oil of lemon eucalyptus can be applied to exposed skin to deter the mites. When using DEET, focus application on the edges of clothing openings, like cuffs, necklines, and waistbands, where chiggers are likely to encounter the barrier. For maximum protection, combining permethrin-treated clothing with DEET applied to the skin is recommended in heavily infested areas.
Physical barriers also play a role in prevention, as chiggers typically attach to lower extremities and migrate upward. Wearing long pants and long-sleeved shirts made of tightly woven fabric creates a physical shield. Tucking pant legs into socks or boots and ensuring cuffs and collars are buttoned tightly minimizes access points for the larvae.