What They Are: Parasitic insects that take up residence on the scalp and hair. They attach their eggs to the base of individual hairs, and happily complete their life cycle (nit, nymph, adult) on the human head in one to three weeks.
Yuck Factor: High. Visible, bloodsucking insects living in a colony on your kid's head? Just thinking about it is enough to make you scratch your head like crazy. Add in the inherent stigma (these are, after all, the original cooties) associated with a lice infestation, and you're guaranteed a case of the heebie-jeebies.
How They Spread: These critters move from head to head, hat to head, pillow to head, comb to head...if it's been on someone's lice-ridden melon, it's a possible vector. Lice can live for a couple of days without human contact, so that baseball cap your kid scored from his new friend at camp could be the source of his buggy hair.
How You Know He's Got Them: All you've got to do is look. The adult lice are about the size of a pinhead -- you can see their little heads and legs if you're brave enough to examine closely. The nits are tiny, yellowish ovals that cling to individual hair shafts; they're most common on the hair behind the ears and near the neck. (Nits look a bit like dandruff but stick tight if you try to brush them off.) Lice bites itch, and kids can feel the wee beasties crawling around (wah!) if they've got a really bad case.
What To Do: Oh, boy. Most doctors agree that using a pesticide shampoo is most effective (you can nit-pick for appearance's sake). For an alternative route, you can try remedies like olive oil, tea tree oil, or petroleum jelly, which may suffocate the lice; there are also any number of nontoxic products, such as Happyheads. Wash all bedding, clothes, and hairbrushes (at 130°F), vacuum rugs and upholstery, and seal away stuffed animals for two weeks.