Head lice like warmth, blood, and close contact with human hair. They are highly specialized parasites that have evolved to live on the human scalp and nowhere else, feeding exclusively on human blood several times a day. Understanding what attracts and sustains lice can help you prevent infestations and clear up some persistent myths about who gets them and why.
Blood Is Their Only Food Source
An adult female louse feeds three to five times per day, piercing the scalp with tiny mouthparts to draw blood. Each feeding session takes in a remarkably small amount, roughly 0.00016 milliliters, but a heavy infestation involving thousands of lice can add up. In rare, extreme cases, researchers have documented infestations large enough to cause iron deficiency anemia from cumulative blood loss.
This blood dependency is what keeps lice tethered to the human head. An adult louse that falls off will die within one to two days without a meal. Young lice, called nymphs, are even more fragile and survive only a few hours away from a host. Lice eggs (nits) need the steady warmth of the scalp to develop. Once separated, they typically die within a week because they can’t maintain the temperature needed to hatch.
Clean Hair vs. Dirty Hair
One of the most stubborn myths about lice is that they prefer dirty hair. They don’t. Lice feed on blood drawn from the scalp, not on oil, dirt, or hair products. A freshly shampooed head is just as appealing to a louse as one that hasn’t been washed in days. There is no link between personal hygiene and the likelihood of getting lice, and anyone with hair can become a host.
Hair Characteristics That Matter
While cleanliness doesn’t play a role, certain physical properties of hair do influence how easily lice can grab on and establish themselves. Research on schoolchildren found that longer hair and a smaller hair diameter both increase the risk of infestation. Thinner strands appear to make it easier for young nymphs to grip the hair shaft with their claw-like legs. Hair color, hair shape (straight, wavy, curly), and the texture of the outer hair scales also contributed to differences in susceptibility, suggesting that lice infestation patterns have more to do with the physical geometry of hair than with gender or behavior alone.
This helps explain why certain populations experience different infestation rates. It’s not about who is “cleaner” but about whose hair a louse can physically cling to most easily.
The Scalp Environment They Need
Lice thrive in a narrow environmental range. The human scalp sits at roughly 35°C (95°F) with consistent humidity from skin moisture, and that’s precisely what lice and their eggs require. Nits are glued to hair shafts close to the scalp, within a few millimeters, because that’s where the temperature is right for embryo development. Eggs laid farther from the scalp or on shed hairs rarely hatch.
The glue itself is remarkably engineered. Female lice secrete a liquid adhesive from specialized glands during egg-laying. This glue contains two structural proteins that are chemically cross-linked by an enzyme, hardening into a rigid sheath that encases both the egg and the hair shaft. The result is a cement so strong that nits can’t be shaken loose or washed off with regular shampooing. The cross-linking process also seals in moisture, which the developing embryo needs to survive. When researchers blocked the enzyme responsible for this hardening, the eggs failed to hatch.
How They Spread
Lice crawl at a top speed of about four inches per minute. They cannot jump or fly. Each of their six legs ends in a hook-shaped claw designed to grip individual hair strands, which makes them excellent climbers but poor travelers on flat surfaces. Head-to-head contact is by far the most common route of transmission: when two people’s hair touches, a louse can bridge the gap and crawl from one head to another.
Spread through shared objects like hats, scarves, or hoodies is possible but uncommon. Lice are not comfortable off the head, and their short survival time away from a host limits this risk significantly. Swimming pools are another source of worry that turns out to be largely unfounded. In one study, lice submerged in chlorinated water for 20 minutes entered a state of complete stillness but revived within about a minute of being removed. They survived concentrations of chlorine well above standard pool levels. However, during submersion, the lice gripped tightly to the hair and did not detach or float away. When naturally infested individuals swam in a chlorinated pool for 30 minutes, no lice transferred between swimmers and none were lost into the water.
Who Gets Lice Most Often
Children between the ages of 4 and 12 are the most frequently affected group. This has everything to do with behavior: young children play in close physical contact, share dress-up clothes, and put their heads together constantly. In one large study of nearly 6,200 kindergarten and school-aged children in Belgium, the point prevalence of active infestation was about 9 percent when detected using thorough wet combing. Outbreaks tend to spike when children return to school after summer breaks.
Adults can absolutely get lice, but it happens less often because adults tend to maintain more physical distance from others. Parents and caregivers of young children are the most likely adult hosts, typically picking up lice during close contact like reading together, hugging, or helping with hair.
Scents and Natural Repellents
Some essential oils do appear to have real effects on lice, not just as repellents but as treatments. A clinical trial tested a solution containing eucalyptus oil and lemon tea tree oil against a standard chemical treatment in children with active infestations. The essential oil solution cured 83 percent of participants who completed the full treatment protocol, compared to just 36 percent for the conventional product. In a separate arm of the same study, a single application of the oil solution killed all 1,418 collected lice within 30 minutes and prevented 100 percent of treated eggs from hatching.
These results are striking, though they reflect a specific formulated product rather than dabbing essential oils on a child’s head at home. Concentration, application method, and repeated treatments all matter. Still, the findings suggest lice are genuinely vulnerable to certain plant-derived compounds, which may help explain the popular belief that lice “dislike” tea tree and eucalyptus scents.