My son came home with lice. Should I treat the whole family with lice shampoo even if I do not see them on everyone's head?

The bane of many parents, the head louse is a tiny, wingless parasitic insect that lives among human hairs and feeds on extremely small amounts of blood drawn from the scalp. Although they may sound gross, lice (the plural of louse) are a very common problem, especially for kids ages 3 years to 12 years (girls more often than boys). Lice aren't dangerous and they don't spread disease, but they are contagious and can just be downright annoying.

Their bites may cause a child's scalp to become itchy and inflamed, and persistent scratching may lead to skin irritation and even infection. It's wise to treat head lice quickly once the diagnosis is made because they can spread easily from person to person. Though very small, lice can be seen by the naked eye.

Lice eggs (called nits). These look like tiny yellow, tan, or brown dots before they hatch. Lice lay nits on hair shafts close to the scalp, where the temperature is perfect for keeping warm until they hatch.

Nits look sort of like dandruff, only they can't be removed by brushing or shaking them off. Unless the infestation is heavy, it's more common to see nits in a child's hair than it is to see live lice crawling on the scalp. Lice eggs hatch within 1 to 2 weeks after they're laid.

After hatching, the remaining shell looks white or clear and continues to be firmly attached to the hair shaft. This is the stage when it's easiest to spot them, as the hair is growing longer and the egg shell is moving further away from the scalp. Adult lice and nymphs (baby lice).

The adult louse is no bigger than a sesame seed and is grayish-white or tan. Nymphs are smaller and become adult lice about 1 to 2 weeks after they hatch. Most lice feed on blood several times a day, but they can survive up to 2 days off the scalp.

With lice bites come itching and scratching. This is actually due to a reaction to the saliva of lice. However, the itching may not always start right away — that depends on how sensitive your child's skin is to the lice.

It can sometimes take weeks for kids with lice to start scratching. They may complain, though, of things moving around on or tickling their heads. Small, red bumps or sores from scratching.

For some kids, the irritation is mild; for others, a more bothersome rash may develop. Excessive scratching can lead to a bacterial infection (the skin would become red and tender and may have crusting and oozing along with swollen lymph glands). If your doctor thinks this is the case, he or she may treat the infection with an oral antibiotic.

You may be able to see the lice or nits by parting your child's hair into small sections and checking for lice and nits with a fine-tooth comb on the scalp, behind the ears, and around the nape of the neck (it's rare for them to be found on eyelashes or eyebrows). A magnifying glass and bright light may help. But it can be tough to find a nymph or adult louse — often, there aren't many of them and they're able to move fast.

Call your doctor if your child is constantly scratching his or her head or complains of an itchy scalp that won't go away. The doctor should be able to tell you if your child is infested with lice and needs to be treated. Not all kids have the classic symptoms of head lice and may be totally symptom-free.

Also be sure to check with your child's school nurse or childcare center director to see if other kids have recently been treated for lice. If you discover that your child does, indeed, have lice or nits, contact the staff at the school and childcare center to let them know. Find out what their return policy is.

Most usually allow kids to return after one topical treatment has been completed.