For educational purposes only. This page does not provide medical or veterinary advice, diagnosis, or treatment. Always consult a qualified healthcare or veterinary professional before making any health-related decisions.

Ectoparasite (insect)HumanDogCat

Lice

Pediculus humanus capitis / Trichodectes canis / Felicola subrostratus

Size: Visible to naked eye — adults 2–3.5 mm; eggs (nits) approx 0.8 mm

Prevalence

Head lice affect 6–12 million children annually in the US alone

Lice are tiny wingless insects that live on the skin and hair of their host. They are highly host-specific — human lice cannot survive on pets and vice versa. Human head lice (Pediculus humanus capitis) are the most common, especially in school-age children. They feed on blood and lay eggs (nits) cemented to hair shafts close to the scalp.

Lifecycle

Eggs (nits) hatch in 7–10 days. Nymphs mature through three stages over 9–12 days. Adults live about 30 days on the host but die within 1–2 days off the host. Females lay 6–10 eggs per day.

Lice — Pediculus humanus capitis / Trichodectes canis / Felicola subrostratus

Symptoms

Intense itching of the scalp, neck, and ears

Tickling sensation of something moving in hair

Visible nits (white/yellow oval eggs) on hair shafts

Small red bumps on scalp, neck, and shoulders

Sores from scratching (risk of secondary bacterial infection)

Difficulty sleeping (lice are more active in the dark)

In pets: scratching, restlessness, visible lice or nits on fur

Pharmaceutical treatments

Evidence-based medications used by healthcare and veterinary professionals.

Reference only. Medication names, types, and notes are provided for general awareness. Dosage, suitability, and prescribing decisions must be made by a licensed physician or veterinarian.

Permethrin 1% (Nix)

OTC

First-line treatment for head lice. Apply to damp hair, leave 10 minutes, rinse. Repeat in 9 days. Resistance is increasing.

Pyrethrin + piperonyl butoxide (Rid)

OTC

Natural pyrethrin from chrysanthemums. Similar efficacy to permethrin. Do not use on those with ragweed allergy.

Ivermectin lotion (Sklice)

Prescription

Single application, no nit combing required. Highly effective including against permethrin-resistant lice.

Spinosad (Natroba)

Prescription

Highly effective single-application treatment. Kills lice and eggs.

Fipronil / Selamectin (pets)

Veterinary

Spot-on treatments effective against lice in dogs and cats. Treat all pets in the household simultaneously.

Holistic & natural approaches

Traditional, herbal, and integrative approaches for general awareness.

Not a substitute for medical treatment. Natural remedies listed here have not been evaluated by the FDA or equivalent regulatory bodies. Do not use these in place of prescribed treatment. Always consult a qualified healthcare or veterinary professional first.

Wet combing (Nit combing)

Apply conditioner to wet hair and systematically comb with a fine-toothed nit comb every 3–4 days for 2 weeks. Labor-intensive but chemical-free and effective when done thoroughly.

Tea tree oil

Terpinen-4-ol has insecticidal properties. Add 5–10 drops to shampoo or dilute in carrier oil. Some evidence of efficacy; avoid use on young children and cats (toxic to cats).

Dimethicone (silicone oil)

Physical suffocation method — coats and immobilizes lice. Available in some OTC products (Hedrin). No resistance issues. Safe for all ages.

Olive oil or coconut oil

Applied overnight under a shower cap, may suffocate lice. Must be combined with thorough nit combing. Evidence is anecdotal but widely used.

Heat treatment

Wash all bedding, clothing, and stuffed animals in hot water (60°C+) and dry on high heat. Items that cannot be washed should be sealed in a bag for 2 weeks.

Prevention

Avoid head-to-head contact with infected individuals

Do not share combs, brushes, hats, scarves, or hair accessories

Regularly check children's hair, especially after school outbreaks

Teach children not to share personal items

Treat all household members and pets simultaneously if infestation found

Wash bedding and clothing in hot water

Zoonotic risk — low or none

Human lice are species-specific and cannot infect dogs or cats. Pet lice cannot infect humans. No zoonotic risk.

Related parasites

Roundworm

Ascaris lumbricoides / Toxocara spp.

Roundworms are large intestinal nematodes and among the most prevalent parasites on Earth. Adult worms live in the small intestine and can reach 15–35 cm in length. Eggs are shed in feces and can survive in soil for years. In pets, Toxocara species are the most common intestinal parasites and can occasionally infect humans (visceral larva migrans).

Tapeworm

Taenia spp. / Dipylidium caninum / Echinococcus spp.

Tapeworms are flat, ribbon-like segmented worms that attach to the intestinal wall using suckers and hooks. They have no digestive system and absorb nutrients directly through their skin. Adult worms shed egg-filled segments (proglottids) that look like grains of rice. Some species (Echinococcus) can form dangerous cysts in organs.

Giardia

Giardia duodenalis (syn. G. lamblia, G. intestinalis)

Giardia is a microscopic flagellated protozoan that colonizes the small intestine. It exists in two forms: the active trophozoite (pear-shaped, with two nuclei resembling a face) and the hardy cyst form that can survive in cold water for months. It is a leading cause of waterborne diarrheal illness worldwide.

This information is for educational purposes only and is not a substitute for professional medical or veterinary advice. If you suspect a parasitic infection, consult a qualified healthcare or veterinary professional.