Spinosad is a prescription topical suspension (0.9%) that kills both live lice and their eggs, often in a single treatment. It comes in a 120 mL bottle, is applied to dry hair, left on for 10 minutes, then rinsed with warm water. Unlike many over-the-counter lice treatments, spinosad eliminates the need for nit combing in most cases, which makes it one of the more straightforward prescription options available.
How Spinosad Kills Lice
Spinosad works by overstimulating the nervous system of lice. It mimics a natural signaling chemical at nerve junctions, causing electrical impulses to fire continuously without stopping. The lice can’t shut down these signals, so they go through a period of hyperexcitation followed by neuromuscular fatigue, paralysis, and death.
What sets spinosad apart from older treatments like permethrin is that it kills lice at every life stage, including eggs (nits) that haven’t hatched yet. Because it’s both pediculicidal (kills live lice) and ovicidal (kills eggs), you’re not relying on a second treatment to catch newly hatched lice the way you would with permethrin-based products.
Step-by-Step Application
Before you start, make sure hair is completely dry. Do not wash or wet hair first. Shake the bottle well.
- Cover the scalp. Apply enough spinosad directly to dry scalp and hair to thoroughly coat the entire area. Work it through the hair from the roots to the tips. For thick, medium-length, or long hair, you may need the entire 120 mL bottle.
- Wait 10 minutes. Leave the product on the hair and scalp for a full 10 minutes. Set a timer so you don’t cut it short.
- Rinse thoroughly. Use warm water to rinse the product completely out of the hair. You can then wash with your regular shampoo if you’d like.
That’s the core process. You do not need to use a fine-toothed nit comb afterward. Spinosad kills eggs in place, so the tedious combing session that most parents dread with other lice treatments is generally unnecessary.
Do You Need a Second Treatment?
Most people only need one application. However, if you still see live lice seven days after the first treatment, apply a second round using the same steps. Do not apply it a third time without checking with your prescriber. Two treatments, spaced seven days apart, is the maximum recommended course.
Because spinosad is ovicidal, the need for a second treatment is less common than with permethrin or pyrethrin-based products, which typically require a mandatory second application regardless of whether live lice are still present.
Who Can Use It
Spinosad is FDA-approved for children 6 months of age and older, as well as adults. It is available by prescription only, so you’ll need to see a healthcare provider to get it.
For infants under 6 months, spinosad is not recommended. The formulation contains benzyl alcohol as an ingredient, and very young infants, particularly premature newborns, cannot metabolize benzyl alcohol efficiently. In premature neonates, benzyl alcohol can accumulate and cause serious toxicity. This concern is specific to very young babies and does not apply to older children or adults using the product topically as directed.
Side Effects
Spinosad is well tolerated overall. The most commonly reported side effects in clinical trials, occurring in more than 1% of users, were redness at the application site and eye redness. Some children also experienced mild itching or irritation where the product was applied. In a safety study of children aged 6 months to 4 years, the most common reactions were mild fever, itching at the application site, and redness.
If the product gets into your eyes, rinse them immediately with water. The eye redness reported in studies was generally mild and temporary.
Tips for Best Results
A few practical things can make the treatment more effective and less messy. First, apply it over a sink or in the bathroom, because the suspension is a slightly orange-colored viscous liquid that can drip. Have a towel ready to catch any runoff around the hairline and neck.
Second, make sure you use enough product. Underapplying is the most common reason any topical lice treatment underperforms. Every strand should be coated from root to tip, and the scalp itself needs full coverage. If the hair is thick or past shoulder length, expect to use the whole bottle on one person.
Third, check all household members. If one person in the home has lice, others may too. Treating only the person with visible lice while ignoring close contacts often leads to reinfestation within days. Wash bedding, hats, and recently worn clothing in hot water and dry on high heat. Items that can’t be washed can be sealed in a plastic bag for two weeks, which outlasts the lice life cycle.
Finally, keep in mind that itching can persist for a few days after successful treatment. Dead nits may remain attached to hair shafts and will eventually grow out. Their presence doesn’t mean the treatment failed. The key indicator of success is the absence of live, crawling lice seven days after application.