Infants can face a wide range of health issues in their first year, from common and easily managed conditions like jaundice and reflux to more serious concerns like respiratory infections and congenital heart defects. Most of these issues are either preventable or treatable when caught early, which is why knowing what to look for matters so much during this vulnerable period.
Jaundice
Jaundice occurs in most newborns. It happens when a pigment called bilirubin builds up in the blood faster than a newborn’s immature liver can process it, turning the skin and whites of the eyes yellow. In most cases, jaundice is mild and resolves on its own within a week or two as feeding increases and the liver matures.
When bilirubin levels climb too high, treatment with phototherapy (special blue lights that help break down bilirubin through the skin) is effective and straightforward. Babies readmitted to the hospital for jaundice typically have bilirubin levels around 18 mg/dL or higher. If levels reach 25 mg/dL or above, it’s considered a medical emergency requiring immediate intensive phototherapy. At that point, bilirubin can drop as much as 10 mg/dL within a few hours under treatment. Untreated severe jaundice can cause brain damage, but this outcome is rare with proper monitoring.
Respiratory Infections and RSV
Respiratory syncytial virus (RSV) is one of the most common respiratory infections in infants and a leading cause of hospitalization in babies under one year. About 2 to 3 out of every 100 infants younger than 3 months are hospitalized with RSV each year.
Early symptoms include a runny nose, coughing, and reduced interest in eating or drinking. In very young babies under 6 months, the signs can look different: irritability, decreased activity, and apnea (pauses in breathing lasting more than 10 seconds). Many infants with RSV won’t develop a fever, which can make it harder for parents to recognize. The cough may progress to wheezing or visible difficulty breathing, which is the point where medical attention becomes urgent.
A preventive antibody treatment for RSV is now part of the recommended immunization schedule, typically given at birth or between 8 and 19 months depending on timing and maternal vaccination status.
Reflux and GERD
Spitting up is normal in babies. Gastroesophageal reflux, where stomach contents come back up into the esophagus, is extremely common and usually harmless. Most babies outgrow it by their first birthday.
The concern arises when reflux becomes gastroesophageal reflux disease (GERD), a more severe form that causes persistent symptoms or complications. Infants with GERD may refuse to eat, spit up frequently, and gain weight more slowly than expected. In some cases, the repeated exposure of stomach acid to the esophagus causes inflammation, which can lead to ulcers and bleeding in the esophageal lining. If your baby is consistently refusing feeds, seems to be in pain during or after eating, or isn’t gaining weight, that pattern points toward GERD rather than ordinary spit-up.
Whooping Cough (Pertussis)
Pertussis is especially dangerous for infants, who are too young to be fully vaccinated against it. The disease progresses through three stages. The first week looks like a mild cold: sneezing, runny nose, low fever, and a light cough. By the second week, the signature paroxysmal coughing fits begin, with intense episodes that can last two to six weeks. Recovery in the third phase takes up to four additional weeks, with coughing gradually decreasing.
The numbers for young infants are sobering. In a multicenter study of confirmed pertussis cases (83% of whom were under 3 months old), 43% required mechanical ventilation and 9.4% died. Vaccination with DTaP begins at 2 months, with follow-up doses at 4 and 6 months. Pregnant individuals are encouraged to get vaccinated during pregnancy so that protective antibodies pass to the baby before birth.
Congenital Heart Defects
Heart defects are the most common type of birth defect, affecting nearly 1% of all births in the United States, or about 40,000 babies per year. About 1 in 4 of those babies has a critical heart defect that requires surgery or other intervention in the first year of life.
Signs to watch for include blue-tinted lips or fingernails, fast or labored breathing, tiring easily during feeding, and unusual sleepiness. Newborn screening now includes pulse oximetry, a painless bedside test that clips onto the baby’s foot and measures blood oxygen levels. Low oxygen can be an early indicator of a heart defect that isn’t visible on the outside. This screening catches many critical defects before symptoms become obvious.
Eczema
Atopic dermatitis (eczema) affects 5% to 20% of children worldwide and frequently appears in the first few months of life. It shows up as dry, red, itchy patches of skin, often on the cheeks, scalp, and creases of the elbows and knees.
Flare-ups can be triggered by environmental factors like dry air, irritating fabrics, and the mechanical damage caused by repeated scratching. Keeping skin consistently moisturized with fragrance-free emollients is the foundation of management. For flares that need more than moisturizer, prescription topical treatments are available for babies as young as 3 months. Infants with severe eczema are also at higher risk for developing food allergies, which is why current guidelines recommend introducing common allergens like peanut and cooked egg around 4 to 6 months rather than delaying them.
Food Allergies
Food allergies affect a growing number of infants, and severe eczema is one of the strongest predictors. For high-risk babies (those with existing food allergies or severe eczema), expert consensus now recommends introducing allergenic foods at around 4 to 6 months to reduce the chance of allergy developing. This is a significant shift from older advice that recommended delaying these foods.
Peanut should be given in age-appropriate forms (thinned peanut butter or peanut puffs, never whole peanuts). Egg should be well-cooked, not raw or lightly pasteurized. Signs of an allergic reaction include hives, swelling of the face or lips, vomiting, and in severe cases, difficulty breathing. Starting these foods at home during a time when you can monitor your baby for a couple of hours afterward is a practical approach.
Dehydration
Newborns and young infants are particularly vulnerable to dehydration because of their small body size and high fluid needs relative to their weight. The most reliable way to track hydration at home is by counting wet diapers. For babies from birth to 4 months, fewer than 6 wet diapers in a 24-hour period is a sign of dehydration.
Other signs include a dry mouth, no tears when crying, a sunken soft spot on the top of the head, and unusual drowsiness. Dehydration in infants often happens during illnesses that cause vomiting, diarrhea, or reduced feeding. It can escalate quickly, so a noticeable drop in wet diapers combined with any of these other signs warrants prompt medical evaluation.
Fever in Young Infants
A rectal temperature of 100.4°F (38.0°C) or higher in a baby under 2 months old triggers a full medical evaluation. At this age, a baby’s immune system is immature enough that even a low-grade fever can signal a serious bacterial infection. The threshold isn’t high because it doesn’t need to be: any confirmed fever in this age group is treated as potentially significant.
For babies older than 2 months, fever is still worth watching but is more commonly caused by viral infections and is less likely to indicate something dangerous. The baby’s behavior, feeding patterns, and overall appearance matter as much as the number on the thermometer.
Sleep-Related Risks
Sudden infant death syndrome (SIDS) and other sleep-related deaths remain a leading cause of infant mortality. Black and Native American/Alaska Native infants die from sleep-related causes at rates more than double those of white infants, driven partly by systemic inequities in access to safe sleep environments and education.
The core safe sleep recommendations from the American Academy of Pediatrics are specific and evidence-based:
- Back sleeping only: Place infants on their backs for every sleep, including naps.
- Own sleep space: Use a crib, bassinet, or portable play yard with a firm, flat mattress and a fitted sheet. No bed-sharing.
- Empty sleep surface: No loose blankets, pillows, stuffed animals, or bumper pads.
- Avoid couches and recliners: Falling asleep with a baby on a couch or armchair is one of the highest-risk situations.
- Avoid seating devices for sleep: Swings and car seats (outside the car) are not safe sleep surfaces.
Breastfeeding and avoiding smoking both independently lower the risk of sleep-related death.
Developmental Delays
Not all infant health issues are diseases or infections. Developmental delays, where a baby isn’t reaching motor, social, or communication milestones on the expected timeline, can be among the earliest signs of underlying conditions like cerebral palsy, autism spectrum disorder, or hearing and vision problems.
Milestones like a first social smile (around 2 months), reaching for objects (around 4 months), sitting without support (around 6 months), and waving or responding to their name (around 9 to 12 months) serve as guideposts. Missing one milestone isn’t necessarily alarming, but missing several, or losing skills a baby previously had, is a clear reason to seek evaluation. Early intervention services, which are available in every state, can begin well before a formal diagnosis and make a measurable difference in outcomes.
Vaccinations in the First Year
The immunization schedule in the first 12 months protects against a long list of serious diseases. Here’s what to expect:
- Birth: Hepatitis B (first dose), RSV preventive antibody (depending on maternal vaccination)
- 2 months: DTaP, Hib, pneumococcal, polio, rotavirus, hepatitis B (second dose)
- 4 months: DTaP, Hib, pneumococcal, polio, rotavirus (second doses)
- 6 months: DTaP, pneumococcal, polio, hepatitis B (third doses), influenza (first dose, annually from here)
- 12 months: MMR, varicella, hepatitis A (first doses), plus catch-up doses of earlier vaccines
This schedule is timed to provide protection during the windows when infants are most vulnerable. Rotavirus vaccination, for example, starts early because the virus causes severe diarrhea and dehydration that is most dangerous in the youngest babies. The DTaP series begins at 2 months because pertussis, as noted above, is life-threatening for unvaccinated infants.