"Itch" - what is it, definition of the term
Pruritus is a sensory phenomenon that elicits an urge to rub or scratch the skin, arising when peripheral nerve endings are stimulated by chemical mediators released in response to irritants, allergens, or parasitic arthropods such as ticks, bugs, lice, and fleas.
Detailed information
Pruritus caused by ectoparasites manifests as localized or widespread skin irritation that prompts a reflexive desire to scratch. The sensation originates from the activation of peripheral nerve fibers (C‑fibers) by chemical mediators released during the parasite’s feeding process. Histamine, proteases, and prostaglandins produced by the insect’s saliva trigger inflammation, leading to erythema, edema, and heightened sensory nerve activity.
Ticks embed their mouthparts into the dermis for several days, delivering saliva that contains anticoagulants and immunomodulatory proteins. These substances suppress local immune responses while simultaneously provoking a persistent itch that may persist for weeks after removal. The prolonged exposure increases the risk of secondary bacterial infection and can serve as a vector for pathogens such as Borrelia burgdorferi.
Bugs, including bed bugs and sand flies, bite intermittently, injecting anticoagulant-rich saliva that produces a rapid, sharp pruritic response. The reaction typically peaks within 24 hours and may be accompanied by papular wheals. Repeated exposure can lead to sensitization, resulting in larger, more inflamed lesions upon subsequent bites.
Lice infest the scalp, body, or pubic region and feed on blood several times per day. Their saliva contains enzymes that irritate the epidermis, causing an incessant itching sensation that intensifies at night. Continuous scratching can cause excoriations, secondary infection, and, in severe cases, crusted pediculosis.
Fleas bite quickly, delivering a small volume of saliva that triggers immediate itching and the formation of red, punctate lesions. The reaction may spread to surrounding areas due to hypersensitivity. Flea‑induced pruritus is often compounded by allergic dermatitis in sensitized individuals.
Management strategies focus on interrupting the itch–scratch cycle and addressing the underlying infestation:
- Remove the parasite mechanically or with approved topical agents.
- Apply topical corticosteroids or calcineurin inhibitors to reduce inflammation.
- Use oral antihistamines to block histamine receptors and diminish sensory signaling.
- Maintain skin hygiene; cleanse affected areas with mild antiseptic solutions to prevent bacterial colonization.
- In cases of vector‑borne disease risk, initiate appropriate antimicrobial therapy promptly.
Understanding the pathophysiology of parasite‑induced pruritus enables targeted treatment, minimizes complications, and reduces the likelihood of recurrent infestations.