Signs and Symptoms of Chigger Bites
Chigger bites present as intensely pruritic erythematous papules and papulovesicles that are characteristically clustered in groups at sites where clothing fits tightly or skin folds exist. 1
Primary Clinical Presentation
Intense pruritus is the hallmark symptom, resulting from the combination of digestive enzymes secreted by the mite larvae and the host's immune response 2
Lesions appear as pruritic erythematous papules and papulovesicles that are self-healing within a couple of weeks in most cases 3
Bites are typically clustered in groups rather than isolated lesions, distinguishing them from many other insect bites 1
Distribution Pattern
Bites occur preferentially in areas where clothing fits tightly (waistbands, sock lines, underwear elastic) or where skin folds exist 1
This pattern reflects the chigger's tendency to attach where skin is thin and access is facilitated by tight clothing 1
Exposure typically occurs during outdoor activities in high grass, weeds, and low brush, with peak season from April through September 1
Immune Response Characteristics
Repeated exposures lead to progressively more intense cutaneous reactions, with initial exposures often producing minimal macroscopic changes 4
Third and fourth exposures can produce marked reactions consisting of erythema, epidermal thickening, and serous exudation with infiltrates of lymphocytes, eosinophils, basophils, and neutrophils 4
The immune response involves both Arthus-type and delayed-type hypersensitivity reactions to chigger antigens 4
Critical Differential Diagnosis
Distinguish chigger bites from tick bites, as tick bites may require consideration of tickborne rickettsial diseases requiring antibiotic therapy 1
The absence of systemic symptoms helps differentiate simple chigger dermatitis from tickborne illness 1
Be aware that certain chigger species can vector Orientia species causing scrub typhus, which presents with fever, malaise, headache, and myalgia—distinct from simple chigger dermatitis 1
Common Pitfalls
Do not misdiagnose the allergic swelling and erythema as cellulitis, which would lead to unnecessary antibiotic use 5
Most early swelling after chigger bites is IgE-mediated allergic inflammation, not infection 5
True infection indicators include progressive redness, increasing pain (not just pruritus), purulent discharge, fever, warmth, and tenderness to palpation 5