9 infant illnesses to watch for (and when to worry)

Researchers are using brain scans to determine if babies are in pain.

The first couple of years of children's lives are full of discoveries for their parents.

You'll learn about their personalities, their favorite foods and what makes their faces light up. However, that time can also be a little unsettling due to some common ailments that infants often encounter within the first few years of their lives.

Here's a list of nine illnesses a new parent might want to monitor and suggestions on when to seek medical help:

WebMD recommends seeing a doctor immediately if your child develops a fever over 100.4 F when he is less than three months old.

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Credit: ajc.com

Hand, Foot and Mouth Disease
Hand, foot and mouth disease starts with symptoms like a sore throat, reduced appetite and fever. Within 24 to 48 hours, small red spots start to develop. Eventually those spots will blister and become painful sores that affect the mouth, palms and the soles of the feet for about seven days.
When to call the doctor: If you notice your child's symptoms getting worse or if they are unable to drink fluids, the Mayo Clinic recommends seeing a doctor.

Fifth DiseaseFifth Disease starts as a low fever accompanied by mild cold-like symptoms, per the health site KidsHealth.org . A few days later, a bright red rash appears on the face and then spreads to other parts of the body. The marks are often itchy.
When to call the doctor: If your child has a wide-spread rash with a fever or cold-like symptoms, you should schedule a visit to a doctor.

PinkeyeIf you notice watering, redness or swelling of the whites of your child's eyes, he or she probably has conjunctivitis, better known as pink eye, a condition caused by allergens or by bacteria. The bacterial form is highly contagious, so be sure to wash your hands regularly. When to call the doctor: Baby Center recommends bringing your child to the doctor at the first sign of pink eye symptoms.

Respiratory Syncytial Virus (RSV)
WebMD defines RSV as "a common, and very contagious, virus that infects the respiratory tract of most children before their second birthday." Signs of infection include cold-like symptoms such as a cough or runny nose that lasts for one or two weeks. 
When to call the doctor: If your child is refusing to feed, is unusually inactive, is having trouble breathing, is coughing up discolored mucus, or is showing signs of dehydration, it may be a good idea to make an appointment to see a doctor.

RoseolaA sudden, high fever is the first sign of roseola. The fever might also come with a sore throat, mild diarrhea, runny nose or cough. Once the fever breaks, small pink spots or patches might appear; possibly with a white ring around some of the spots. Roseola rashes are not itchy and only last for a few hours or days.
When to call the doctor: If your child's fever exceeds 103 degrees Fahrenheit  or lasts more than a week, it might be time for a doctor appointment. You should also make a call if a rash doesn't clear up after three days.

Viral GastroenteritisCommonly called a stomach flu, viral gastroenteritis can be identified by fever, watery diarrhea, pain or cramping in the abdomen and vomiting.
When to call the doctor: Healthline recommends seeking emergency medical treatment if your child is dehydrated, has blood in their diarrhea or has diarrhea for three days or more.

Ear Infection
Per parenting.com, your child might have an ear infection if they show symptoms such as crankiness, unwillingness to lie flat and crying during feeding. The presence of allergens, like cigarette smoke or animal dander, can trigger an infection.
When to call the doctor: If you suspect your child has an ear infection, it might be wise to have a doctor check their ears since too many untreated ear infections can lead to future health concerns.

Influenza
Flu symptoms include fever, cough, sore throat, runny nose and fatigue. Infection spreads easily, as people are often contagious before showing any signs of illness.
When to call the doctor: Parents Magazine recommends getting your child an annual flu vaccine to avoid this illness. However, if they start showing symptoms, you might want to see a doctor right away.

FeverIf your child's body temperature spikes suddenly, it is likely that he has a fever. A fever is a common symptom of a number of illnesses. If the fever is accompanied by dehydration, a rash or trouble breathing, it could be a sign of a serious illness.
When to call the doctor: If your child develops a fever over 100.4 degrees Fahrenheit when they are less than three months old, WebMD recommends seeing a doctor immediately.