Your baby's immune system is still developing and she is susceptible to a host of viruses. Here are some of the more common ones and their treatments.

Diarrhea

In babies, vomiting and diarrhea are usually caused by viruses. Wash your hands often as viral diarrhea is very contagious. If vomiting and diarrhea continue after several feedings, your baby risks dehydration.

If you are breastfeeding and your baby has diarrhea, nurse more frequently. If you are formula-feeding, switch to Pedialyte or a comparable nonprescription oral rehydration fluid that will replenish electrolytes in addition to lost fluids. (Don't use sports drinks; they contain too little sodium and oftentimes large amounts of sugar.) These rehydration fluids come plain or flavored and are available without a prescription. Stick to the plain; most babies find the flavored versions unpalatable. (You can also try freezing it in popsicle form.)

Try to get your baby to drink four ounces of the solution every time she has a watery movement. Switch back to formula if the diarrhea becomes less watery and your baby is peeing regularly. Some moms have had success treating diarrhea with barley or rice water (cook rice or barley until very soft, then strain out the grain and put the remaining liquid in a bottle, adding one-quarter teaspoon of salt to every two cups of water).

If your baby seems listless, is urinating a lot less than usual, cries with few tears, has a sunken fontanel (soft spot), or the diarrhea lasts longer than a few days, call your doctor.

Vomiting

Sometimes it's hard to tell the difference between normal spit-up and vomiting. It can seem like a lot of what you've just put into your baby has come back out and is all over you. Some babies spit up a lot because they gobble their food and inhale a lot of air that produces bubbles and gas.

Here's a basic rule of thumb: spit happens. It's a result of a weak and immature valve between the stomach and esophagus that usually resolves itself by the time your baby is a year old. The spit-up often comes with a burp.

Vomiting, on the other hand, is much more forceful, involves most, if not all, of the feeding, and can upset your baby. Your baby may run a fever.

If your baby is vomiting, spread towels over vulnerable surfaces. Reduce nursing time, but not frequency, with your breastfed baby. If she vomits once or twice, nurse on only one side every hour or two; if she vomits more than twice, nurse for five minutes every thirty to sixty minutes. Return to your regular feeding pattern after eight hours without vomiting. For a formula-fed baby, switch to one of the rehydration fluids and give a teaspoonful of fluid every ten minutes, increasing the amount after four vomit-free hours. Resume normal feeding after eight hours (at which point you can start dealing with the piles of laundry).

Contact a physician if:

• There are signs of dehydration, such as no urine in over eight hours.

• Any blood appears in the vomit.

• There seems to be abdominal pain that lasts for more than four hours.

• The vomiting continues for more than twenty-four hours.

• Your baby just seems really, really sick.

• You are concerned and your instinct tells you something is wrong.

Ear Infections

Unlike stomach viruses that announce themselves clearly (and messily), ear infections are harder to identify, at least until your child is old enough to say “Hurts” as she points to her ear. She may pull on her ear or bat at it — but some babies do that anyway. She will probably be cranky, particularly when you try to lay her down, and may have trouble sleeping — but some babies are like that anyway. And she may eventually get a fever or have a runny nose for a few days.

Your doctor will look in your baby's ear and, if the ear is infected, will see a red ear drum that is bulging with the pressure of trapped fluid. If your doctor decides to prescribe antibiotics, the good news is that you'll often see a change in your baby's behavior within forty-eight hours. If the doctor wants to wait a day or two because signs of infection are minimal, don't push for unnecessary antibiotics.

To make your baby more comfortable in the meantime, give her acetaminophen or ibuprofen to dull the pain and soothe her ear with warm compresses. Wet a washcloth with warm tap water, wring it out, hold it over the ear, and keep her in a sitting position. Bring in her car seat and let her sleep in that or in the stroller. Pile pillows or books under the head end of the mattress if she's in her crib. (Lying horizontally increases the pressure on the ear.) Ask your doctor to prescribe anesthetic ear drops to numb the pain.

Some babies get ear infections constantly — whenever, it seems, they get a cold. This can be more than a nuisance since an ear infection may muffle your baby's hearing just when she is learning to speak. Children usually outgrow ear infections as their Eustachian tubes enlarge, become firmer, and have improved drainage.

Chronic ear infections can also be treated by a tympanostomy (insertion of drainage tubes in the eardrums) or the removal of tonsils or adenoids. Both procedures are performed under anesthesia, but at much lower levels than what's required for general surgery. A laser treatment that puts a hole in the eardrum for drainage and can be performed with just a topical anesthetic has been approved, but isn't in wide use.

A vaccine called Prevnar (or PCV, for pneumococcal conjugate vaccine), intended for prevention of bacterial meningitis, blood infections, and pneumonia, protects against some ear infections as well. This vaccine is universally recommended by the Centers for Disease Control and Prevention and the AAP for children at two, four, and six months, and again between twelve and fifteen months.

Croup

Croup is one of the scarier viruses, although it sounds much worse than it actually is. It seems to come on suddenly, usually in the middle of the night. You'll know croup when you hear it — your baby will sound like a seal barking. Croup usually lasts for five to six days, with the worst symptoms at night. Use a cool humidifier in the bedroom or hang up wet towels as dry air makes croup worse.

In severe cases you may hear a raspy, vibrating sound when your baby inhales between coughs, and breathing becomes difficult. If this happens, race her into the bathroom and stand outside the shower, turning it on full blast as hot as it can go. You want the steam that is generated, not the water. The steamy room should ease her breathing. Try to calm her down by singing or reading a story — whatever works best. The more upset she is, the worse her croup will be. If steam immersion works, put a humidifier in her room, crank it up, and put her back to bed You can also bring a quilt into the steamy bathroom and lie down with her on the floor. You can also take her outside — cool, damp air can help her breathing, and the change of scene may calm her down.

Call your doctor immediately if these efforts have no effect after twenty minutes, if she struggles to breathe even when she isn't coughing, or she can't cry because she can't get enough breath.

Asthma

Asthma is the leading cause of chronic illness in children. It can be triggered by allergies or by a virus that inflames the lining of the bronchioles, airway branches of the bronchi that are smaller than one millimeter in diameter. Often the attacks come on at night. The child wakes up, has trouble exhaling, and panics. You may hear wheezing as your baby exhales, or notice the center of her chest, between her breastbones, pull inward when she takes a breath. Call your doctor if the breathing problems seem severe, if she's breathing rapidly (more than forty breaths a minute), or if her lips or fingertips turn blue. Sit your baby up and try to calm her down while talking to the doctor, as crying only makes her struggles to breathe worse.

If allergies and asthma run in your family, talk to your doctor about medication like albuterol (to open airways) and prednisone (a steroid that reduces inflammation of the bronchial tubes). Never administer another family member's medication.

Infectious Rashes

A number of infectious diseases are accompanied by a characteristic, and often uncomfortable, rash. The good news is you probably won't have to take care of a child in itchy distress from measles, rubella, or chickenpox since your child will be vaccinated against those diseases when she turns one. Your antibodies will provide some protection as long as you breast-feed, and until about four months of age if you're bottle-feeding. Nevertheless, your child may still contract coxsackie, roseola, and fifth disease.

Coxsackie

In coxsackie, also called hand, foot, and mouth disease, spots appear inside the mouth and on the hands, feet, and butt. It usually comes with a fever, but the condition rarely causes long-term complications. Your baby will probably be miserable, as the mouth spots often blister making swallowing uncomfortable. Keep nursing your younger baby; you can give an older baby juice popsicles to help soothe her throat. She might be happier drinking from a cup than a bottle and for older babies you can try giving half a teaspoonful of a liquid antacid (like Maalox) before meals to coat the ulcers. A coxsackie bout can last as long as a week — and it makes for a very long week.

Coxsackie is very contagious from about two days before the rash appears until about seven days after, with a three-to six-day incubation period. Because it's hard to prevent spreading this one and it is generally harmless, pediatricians don't advise making yourself crazy quarantining your child.

Roseola

The first symptom of roseola that you'll notice will be a fever as high as 105°F. The fever lasts for three to four days, and there are rarely any other symptoms, so you may have no idea what is wrong. Then the fever will go away and faint pink-red spots appear on your baby's trunk, neck, and arms. This is good news — unlike the other rash diseases, the spots signify the end, not the beginning, of the virus. It is contagious until the rash is gone; the incubation period is about twelve days. Complications from roseola are rare, with the small possibility of a febrile seizure because the baby's temperature spikes fast and high.

Fifth Disease

In fifth disease, also called slapped-cheek disease, your baby's face will be bright red, as if her cheeks were sunburned. The rash travels to the arms and legs, then on to other parts of the body. It usually lasts for a few days but may go on for weeks, reappearing whenever she gets warmer than usual, like when taking a bath. Again, this is a fairly benign virus and causes complications only in pregnant women.

Fifth disease is mainly contagious for a week before the rash appears. Once the rash appears, she is no longer considered contagious. If you believe a pregnant woman has been exposed to your baby, tell her to see her obstetrician. The OB will order an antibody test to determine if the mother was previously protected from the disease or not. If she wasn't, the pregnancy will be monitored closely. Fifth disease doesn't cause birth defects, but some infected fetuses develop severe anemia, and a small percentage die.

Other Rashes

Babies also typically get blotchy, red pimples in their second or third week. This baby acne is normal and goes away on its own. Heat can also cause a rash, particularly around your baby's neck, armpits, or diaper area. Be sure not to overdress her when the weather is hot and humid. To soothe heat-induced rashes, give your baby a cool bath every few hours, letting her skin air-dry. For small areas, lay a cool, damp washcloth over the region for ten minutes or so at a time.