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Chickenpox was once considered a rite of passage for most children. Before 1995 — when a vaccine for chickenpox became available in the United States — about 4 million Americans, mostly children, contracted chickenpox each year. Thanks to the vaccine, the number of cases and hospitalizations is down dramatically.

However, when chickenpox does occur, it's highly contagious among people who aren't immune. The red, itchy rash is caused by the varicella-zoster virus, which is part of a group of viruses called herpesviruses. It spreads easily from person to person through the air and physical contact.

Most people think of chickenpox as a mild disease — and, for most, it is. Chickenpox usually lasts about two weeks and rarely causes complications. But the disease can be serious, even in healthy children.

There's no way to know which infected child or adult will develop a severe case. However, the chickenpox vaccine is a safe, effective way to prevent chickenpox and its possible complications. In the small number of cases when the vaccine doesn't stop chickenpox completely, the resulting infection is much milder than the infections that put most U.S. children into bed for a week years ago.

The best-known sign of chickenpox is a red, itchy rash that breaks out on your face, scalp, chest and back, but it can spread across your entire body, even into your throat, eyes and vagina.

The chickenpox rash usually appears less than two weeks after exposure to the virus and begins as superficial spots. These spots quickly turn into small liquid-filled blisters that break open and crust over. New spots continue to appear for several days and may number in the hundreds. Itching may range from mild to intense.

The rash may be preceded by or accompanied by:

• Fever
• Abdominal pain or loss of appetite
• Mild headache
• General feeling of unease and discomfort (malaise) or irritability
• Mild cough and runny nose the first two days of illness before the rash appears

In healthy children, the disease is generally mild.

Chickenpox is highly contagious to people not immune to it and spreads quickly within child care facilities, schools and families. The virus is transmitted by direct contact with the rash or by droplets dispersed into the air by coughing or sneezing.

A person who has chickenpox can transmit the virus for up to 48 hours before the telltale rash appears and remains contagious until all spots crust over.

People who've been vaccinated against chickenpox are usually immune to the virus. The same is true of anyone who has had chickenpox in the past. People at risk of contracting chickenpox include anyone who hasn't been vaccinated or who has never had the disease.

If you suspect that you or your child has chickenpox, consult your doctor. He or she can easily diagnose chickenpox by examining the characteristic rash and by noting the presence of accompanying symptoms. Your doctor can also prescribe medications to lessen the severity of disease and treat complications, if necessary. Be sure to call ahead for an appointment, to avoid waiting and possibly infecting others in a crowded waiting room.

Also, be sure to let your doctor know if any of these complications occur:

• The rash spreads to one or both eyes.
• The rash gets very red, warm or tender, indicating a possible secondary bacterial skin infection.
• The rash is accompanied by dizziness, disorientation, rapid heartbeat, shortness of breath, tremors, loss of muscle coordination, worsening cough, vomiting, stiff neck or a fever higher than 103 F.

Chickenpox is normally a mild disease. But it can be serious and can lead to complications, especially in these high-risk groups:

• Newborns and infants whose mothers never had chickenpox or the vaccine
• Teenagers
• Adults
• Pregnant women
• People whose immune systems are impaired by another disease or condition
• People who are taking steroid medications for another disease or condition, such as children with asthma
• People with the skin inflammation eczema

The most common complication of chickenpox is a bacterial infection of the skin. Chickenpox may also lead to pneumonia or an inflammation of the brain (encephalitis), both of which can be very serious.

Chickenpox and shingles
Anyone who had chickenpox as a child is at risk of a latent illness called shingles. After a chickenpox infection, some of the varicella-zoster virus may remain in your nerve cells. Many years later, the virus can reactivate and resurface as shingles — a painful band of short-lived blisters. About one in 10 adults who've had chickenpox experiences shingles. The virus is more likely to reappear in older adults and people with weakened immune systems.

Shingles can lead to its own complication — a condition in which the pain of shingles persists long after the blisters disappear. This complication, called postherpetic neuralgia, can be severe.

Chickenpox and pregnancy
Other complications of chickenpox affect pregnant women. Chickenpox early on in pregnancy can result in a variety of problems in a newborn, including low birth weight and birth defects, such as limb abnormalities. A greater threat to a baby occurs when the mother develops chickenpox in the week before birth. Then it can cause a serious, life-threatening infection in a newborn.

If you're pregnant and not immune to chickenpox, talk to your doctor about the risks to you and your unborn child.

In otherwise healthy children, chickenpox typically requires no medical treatment. Your doctor may prescribe an antihistamine to relieve itching. But for the most part, the disease is allowed to run its course.

For people who have a high risk of complications from chickenpox, doctors sometimes prescribe medications to shorten the duration of the infection and to help reduce the risk of complications. If you or your child falls into a high-risk group, your doctor may suggest an antiviral drug such as acyclovir (Zovirax) or another drug called intraveneous immune globulin (IGIV). These medications may lessen the severity of the disease. Other antiviral drugs, such as valacyclovir (Valtrex) and famciclovir (Famvir), also may lessen the severity of the disease, but have been approved for use only in adults. In some cases, your doctor may recommend getting the chickenpox vaccine after exposure to the virus. This can prevent the disease or lessen its severity.

If complications do develop, your doctor will determine the appropriate treatment. Treatment for skin infections and pneumonia may be with antibiotics. Treatment for encephalitis is usually with antiviral drugs. Hospitalization may be necessary.

Don't give anyone with chickenpox — child or adult — any medicine containing aspirin because this combination has been associated with a condition called Reye's syndrome.

The chickenpox (varicella) vaccine is the best way to prevent chickenpox. Experts from the Centers for Disease Control and Prevention (CDC) estimate that the vaccine provides complete protection from the virus for nearly 90 percent of young children who receive it. When the vaccine doesn't provide complete protection, it significantly lessens the severity of the disease.

The chickenpox vaccine (Varivax) is recommended for:

• Young children. In the United States, children receive one dose of the varicella vaccine between 12 and 18 months of age, as part of a routine immunization schedule.
• Unvaccinated older children. Children between 19 months and 13 years of age who haven't had chickenpox should receive one dose of the vaccine.
• Unvaccinated adults who've never had chickenpox but are at high risk of exposure. This includes health care workers, teachers, child care employees, international travelers, military personnel, adults who live with young children and all women of childbearing age. Adults and children older than 13 who've never had chickenpox or been vaccinated usually receive two doses of the vaccine, four to eight weeks apart. If you don't remember whether you've had chickenpox or the vaccine, a blood test can determine your immunity.

If you've had chickenpox, you don't need the vaccine. A case of the chickenpox usually makes a person immune to the virus for life. It's possible to get chickenpox more than once, but it's not common; this may occur if the first episode was during the first six months of life.

The vaccine isn't approved for:

• Pregnant women
• People with weakened immunity
• People who are allergic to gelatin or the antibiotic neomycin

Talk to your doctor if you're unsure about your need for the vaccine. If you're planning on becoming pregnant, consult with your doctor to make sure you're up-to-date on your vaccinations before conceiving a child.

Is it safe and effective?
Parents typically wonder whether vaccines are safe. Since it became available, this vaccine has been given to millions of people. Studies continue to show the vaccine to be safe and effective. Side effects are generally mild and include redness, soreness, swelling and, rarely, small bumps at the site of the shot.

Some vaccines require booster doses. Time and research will tell if Varivax is one of them, though it appears that a booster shot may not be necessary with this vaccine.

To help ease the symptoms of an uncomplicated case of chickenpox, follow these simple self-care measures:

• Don't scratch. Scratching can cause scarring, slow down the healing process and increase the risk that the sores will become infected. If your child can't seem to stop scratching, put gloves on his or her hands, especially at night. And trim his or her fingernails to lessen the amount of damage that can be done. If itching is particularly severe or irritating, talk to your doctor about prescribing an antihistamine for relief.
• Take to the tub. Comfortably cool baths can help relieve itching and provide a playful diversion for a young child. For added relief, sprinkle the bath water with baking soda, uncooked oatmeal or colloidal oatmeal — a finely ground oatmeal that is made for the tub, not the stove.
• Apply lotion. Dabbing the spots with calamine lotion may help relieve the itching.
• Try bed and a bland diet. Getting plenty of rest can help beat any infection. Soft, bland foods can also be helpful if chickenpox sores develop in the mouth. Spicy, acidic or hard and crunchy foods can be irritating to mouth sores.
• Treat a fever. Acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin, others) won't cure chickenpox, but either medication can lower a mild fever. Don't give aspirin to anyone with chickenpox because it can lead to a serious condition called Reye's syndrome. And don't try to treat a high fever without consulting your doctor.