Common Childhood Illnesses A-Z

Adenoviruses are a family of over 50 virus types that cause a wide range of illnesses in children, including upper and lower respiratory infections, conjunctivitis (pink eye), gastroenteritis, and croup. They account for approximately 5-10% of all respiratory infections in children. Adenovirus infections tend to be more severe and prolonged than typical colds, with high fevers lasting 5-7 days. They are extremely common in young children, especially those in daycare or group settings.

Asthma is a chronic inflammatory disease of the airways that causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing. It affects approximately 6 million children in the United States and is the most common chronic disease of childhood. In young children (under 5), it may be called "reactive airway disease" as definitive diagnosis is difficult before this age. Asthma involves airway inflammation, bronchospasm, and mucus production triggered by various stimuli.

Bronchiolitis is a common lower respiratory tract infection in infants and young children, most often caused by RSV. It causes inflammation and congestion in the small airways (bronchioles) of the lungs, leading to wheezing and difficulty breathing. It is the most common reason for hospitalization in infants under 1 year.

Acute bronchitis is an inflammation of the bronchial tubes (large airways) in the lungs, causing a persistent cough that may produce mucus. In children, it is almost always caused by viruses and typically follows a cold or upper respiratory infection. Unlike pneumonia, bronchitis does not affect the small airways or air sacs. It is important to distinguish bronchitis from bronchiolitis (which affects infants) and asthma. Antibiotics are not indicated for acute bronchitis in otherwise healthy children.

The common cold is a viral infection of the upper respiratory tract (nose and throat). Babies get an average of 6-8 colds per year, and those in daycare may get even more. Over 200 different viruses can cause colds, with rhinoviruses being the most common. While uncomfortable, colds are rarely dangerous in healthy babies.

COVID-19 is caused by the SARS-CoV-2 virus and generally causes mild illness in most infants and young children, often resembling a common cold or mild flu. However, some children — particularly those under 1 year old or with underlying health conditions — can develop severe disease. A rare but serious complication called Multisystem Inflammatory Syndrome in Children (MIS-C) can occur 2-6 weeks after infection, causing widespread inflammation affecting the heart, lungs, kidneys, brain, and other organs. Vaccines are available for children 6 months and older.

Croup is a common childhood illness that causes swelling of the voice box (larynx) and windpipe (trachea). It produces a distinctive barking cough that sounds like a seal, along with a harsh squeaky sound when breathing in (stridor). It is most common in children aged 6 months to 3 years.

Enterovirus D68 (EV-D68) is a non-polio enterovirus that causes respiratory illness ranging from mild cold-like symptoms to severe wheezing and respiratory distress. Unlike most enteroviruses, which primarily cause gastrointestinal illness, EV-D68 primarily affects the respiratory tract. It gained national attention in 2014 during a large outbreak that hospitalized hundreds of children across the United States. EV-D68 has been linked to acute flaccid myelitis (AFM), a rare but serious neurological condition causing sudden weakness or paralysis in the limbs, similar to polio. Children with asthma or a history of wheezing are at highest risk for severe respiratory illness.

Influenza (the flu) is a contagious respiratory illness caused by influenza viruses. In babies and toddlers, it can cause more severe illness than a common cold, including high fever, body aches, and extreme fatigue. Children under 5 (especially under 2) are at higher risk for serious flu complications.

Human metapneumovirus (hMPV) is a common respiratory virus first identified in 2001 that causes illness ranging from mild colds to severe bronchiolitis and pneumonia in young children. It is closely related to RSV and causes similar clinical presentations. By age 5, virtually all children have been infected at least once. hMPV is the second or third most common cause of lower respiratory tract infection in young children after RSV. It circulates primarily in late winter and spring.

Human parainfluenza viruses (HPIVs) are a group of four related viruses (HPIV-1 through HPIV-4) that are among the most common causes of respiratory illness in infants and young children. HPIV-1 and HPIV-2 are the leading causes of croup (laryngotracheobronchitis), while HPIV-3 is a major cause of bronchiolitis and pneumonia in infants — second only to RSV. Nearly all children are infected with at least one type of parainfluenza by age 5. Despite the name, parainfluenza viruses are unrelated to influenza (flu) viruses.

Pneumonia is an infection of the lungs that causes inflammation and fluid buildup in the air sacs. In babies, it is most often caused by viruses (RSV, influenza, adenovirus) but can also be bacterial. It can range from mild to serious, especially in infants under 6 months.

Reactive airway disease (RAD) is a term used to describe wheezing episodes in young children (typically under age 5) who are too young to receive a definitive asthma diagnosis. It refers to airways that are overly sensitive and react by narrowing and producing excess mucus in response to triggers such as viral infections, cold air, smoke, or allergens. While many children with RAD outgrow their symptoms by school age, some go on to develop persistent asthma — especially those with a family history of asthma or allergies, personal history of eczema, or allergic sensitization.

RSV is a very common respiratory virus that infects nearly all children by age 2. In most babies, it causes cold-like symptoms, but in infants under 6 months and premature babies, it can cause serious lower respiratory illness including bronchiolitis and pneumonia.

Whooping cough (pertussis) is a highly contagious bacterial infection caused by Bordetella pertussis. It causes severe, uncontrollable coughing fits followed by a high-pitched "whoop" sound when breathing in. It is most dangerous in infants under 12 months who are not yet fully vaccinated, and can be life-threatening in newborns.

Clostridioides difficile (C. diff) is a spore-forming bacterium that can cause diarrhea and colitis. In adults and older children, C. diff infection (CDI) is strongly associated with antibiotic use that disrupts normal gut flora. However, in infants under 12 months, C. diff colonization is extremely common (up to 70% of healthy infants carry C. diff) and is considered part of normal gut flora development — positive stool tests in this age group rarely indicate true disease. The immature infant gut lacks the toxin receptors needed for C. diff to cause illness. C. diff becomes a clinical concern primarily in children over 1-2 years of age, especially following antibiotic use, hospitalization, or in immunocompromised children.

Celiac disease is a chronic autoimmune disorder in which ingestion of gluten (a protein found in wheat, barley, and rye) triggers an immune response that damages the lining of the small intestine. This damage impairs nutrient absorption and can lead to a wide range of symptoms. Celiac disease affects approximately 1 in 100 people worldwide, with a strong genetic component — nearly all affected individuals carry HLA-DQ2 or HLA-DQ8 genes. Symptoms typically appear weeks to months after gluten is introduced to the diet (usually around 6-12 months of age). It requires a lifelong gluten-free diet and is not outgrown.

Cow's milk protein allergy (CMPA) is the most common food allergy in infants and young children, affecting an estimated 2-3% of infants. It involves an abnormal immune response to one or more proteins in cow's milk (primarily casein and whey). CMPA can be IgE-mediated (immediate reactions within minutes to 2 hours), non-IgE-mediated (delayed reactions occurring hours to days later, involving cell-mediated immune mechanisms), or mixed. Non-IgE-mediated CMPA is more common in infants and primarily affects the gastrointestinal tract. Importantly, CMPA can occur in exclusively breastfed infants when cow's milk proteins from the mother's diet pass through breast milk. The majority of children (about 80-90%) outgrow CMPA by age 3-5 years.

Food poisoning (foodborne illness) occurs when a child eats or drinks food contaminated with harmful bacteria, viruses, parasites, or their toxins. Common bacterial causes include Salmonella, E. coli, Campylobacter, and Staphylococcus aureus. Symptoms typically include vomiting, diarrhea, and abdominal cramps. Most cases resolve on their own, but some can be serious in young children.

Gastroenteritis is an inflammation of the stomach and intestines, commonly called the "stomach flu" (though unrelated to influenza). It causes vomiting, diarrhea, and abdominal pain. In infants and young children, the primary concern is dehydration. Most cases are viral (norovirus and rotavirus being the most common causes), though bacterial and parasitic causes also occur.

Giardiasis is an intestinal infection caused by the microscopic parasite Giardia lamblia (also called Giardia intestinalis or Giardia duodenalis). It is one of the most common waterborne parasitic infections worldwide and a frequent cause of diarrheal illness in children attending daycare. The parasite lives in the small intestine and is passed in stool as hardy cysts that can survive in the environment for months. Infants and toddlers are especially susceptible because of frequent hand-to-mouth behavior and diaper-related exposures in group care settings.

Intussusception is a serious condition in which one segment of the intestine telescopes (invaginates) into an adjacent segment, like a collapsing telescope. This causes bowel obstruction, cutting off blood supply to the affected section. It is the most common cause of intestinal obstruction in children between 3 months and 6 years of age, with peak incidence at 5-10 months. It is a medical emergency requiring prompt treatment.

Norovirus is the most common cause of acute gastroenteritis (stomach flu) in people of all ages. It causes sudden onset of vomiting and diarrhea and is extremely contagious. It spreads rapidly through families, daycare centers, and anywhere people are in close contact. While usually self-limiting, it can cause dangerous dehydration in young babies.

Pyloric stenosis is a condition in which the muscle (pylorus) at the outlet of the stomach thickens and swells, blocking food from passing into the small intestine. It causes progressively worsening projectile vomiting in infants, typically presenting between 2-8 weeks of age. It is the most common surgical cause of vomiting in infancy and requires surgical correction.

Rotavirus is a highly contagious virus that causes severe diarrhea and vomiting in infants and young children. Before the vaccine was introduced, it was the leading cause of severe diarrhea in children under 5 worldwide. Even with vaccination, it remains a concern for unvaccinated or partially vaccinated infants. It is the most common cause of severe dehydrating gastroenteritis in young children.

Adenoids are a patch of lymphoid tissue located behind the nose at the very back of the throat (nasopharynx). They are a normal part of the immune system and are largest between ages 2 and 6, naturally shrinking by adolescence. Adenoiditis occurs when the adenoids become infected and inflamed, most often by bacteria such as Streptococcus, Haemophilus influenzae, or Moraxella catarrhalis. Chronic or recurrent infections can cause adenoid hypertrophy (persistent enlargement), leading to nasal obstruction, mouth breathing, snoring, sleep-disordered breathing, and recurrent ear infections. Enlarged adenoids are one of the most common causes of chronic nasal obstruction and obstructive sleep apnea in young children.

Ear infections are one of the most common reasons parents bring young children to the doctor. They occur when fluid builds up behind the eardrum and becomes infected by bacteria or viruses. By age 3, about 75% of children will have had at least one ear infection. They often follow a cold or upper respiratory infection.

Gingivostomatitis is a common infection of the mouth and gums caused by herpes simplex virus type 1 (HSV-1). It typically occurs as the first (primary) HSV-1 infection in young children aged 6 months to 5 years. The condition causes painful ulcers on the gums, tongue, lips, and inside of the cheeks, along with swollen, bleeding gums and fever. It is extremely painful and often leads to dehydration from refusal to eat or drink.

Hand, foot, and mouth disease (HFMD) is a common and highly contagious viral illness most often caused by Coxsackievirus A16 or Enterovirus 71. It causes painful sores in the mouth and a rash with blisters on the hands, feet, and sometimes buttocks. It is most common in children under 5 and spreads rapidly in daycare settings.

Laryngitis is inflammation of the larynx (voice box), causing hoarseness or loss of voice. In young children, it often presents as croup (laryngotracheobronchitis) with a characteristic barking cough and stridor. In older children, it more closely resembles adult laryngitis with hoarseness. Most cases are caused by viral infections (parainfluenza, RSV, adenovirus) and resolve without specific treatment.

A peritonsillar abscess (PTA) is a collection of pus that forms in the tissue beside the tonsil, usually as a complication of untreated or inadequately treated tonsillitis or strep throat. It is the most common deep neck infection in children and adolescents, with peak incidence in teens and young adults. It requires urgent medical treatment and often drainage.

Sinusitis is an infection or inflammation of the sinuses — the air-filled spaces in the bones around the nose. In children, it typically develops as a complication of a viral upper respiratory infection when bacteria invade the swollen, fluid-filled sinus cavities. About 6-9% of colds in children are complicated by bacterial sinusitis. The maxillary and ethmoid sinuses are present at birth, making sinusitis possible even in infants.

Strep throat is a bacterial infection of the throat and tonsils caused by Group A Streptococcus (GAS). While uncommon in children under 3, it becomes more frequent in toddlers and preschoolers, especially those in group childcare. Unlike viral sore throats, strep requires antibiotic treatment to prevent complications.

Swimmer's ear is an infection of the outer ear canal (the tube from the outer ear to the eardrum). It occurs when water remains trapped in the ear canal, creating a warm, moist environment for bacteria to grow. It is different from a middle ear infection (otitis media). Common in children who swim frequently, but can also occur from scratching the ear canal, using cotton swabs, or wearing hearing aids or earbuds.

Tonsillitis is an inflammation of the tonsils, the two oval-shaped pads of tissue at the back of the throat. It is extremely common in children between ages 2 and 15. While viral infections cause most cases, bacterial tonsillitis (especially Group A Streptococcus) requires antibiotic treatment. Recurrent tonsillitis may require surgical removal of the tonsils.

Cellulitis is a common bacterial skin infection affecting the deeper layers of the skin (dermis and subcutaneous tissue). It causes a spreading area of redness, swelling, warmth, and tenderness. In children, it often develops after a break in the skin such as a cut, insect bite, or area of eczema, and is most commonly caused by Staphylococcus aureus or Group A Streptococcus.

Fungal diaper rash is caused by an overgrowth of Candida yeast (most commonly Candida albicans) in the warm, moist diaper area. It differs from regular irritant diaper rash by its bright red appearance, well-defined borders, and characteristic satellite lesions. It often develops after antibiotic use or when regular diaper rash persists beyond 3 days.

Head lice are tiny wingless insects that live on the human scalp and feed on blood. They are extremely common in children ages 3-11 and spread through direct head-to-head contact. While they cause intense itching and are a nuisance, head lice do not carry disease and are not a sign of poor hygiene.

Herpes simplex virus (HSV) causes painful blisters and sores on the skin and mucous membranes. HSV-1 typically causes oral herpes (cold sores) and is the more common type affecting children, while HSV-2 primarily causes genital herpes but can also infect newborns. In babies under 3 months old, herpes simplex is a medical emergency — neonatal herpes can cause devastating brain infection (encephalitis), organ failure, and death if not treated immediately with IV antivirals. In older babies and toddlers, HSV-1 typically presents as cold sores or gingivostomatitis (painful mouth sores) and is generally manageable.

Impetigo is a highly contagious bacterial skin infection common in infants and young children. It causes red sores that can rupture, ooze, and form a distinctive honey-colored crust. It most often appears around the nose, mouth, and on hands, but can occur anywhere on the body.

Molluscum contagiosum is a common viral skin infection caused by a poxvirus. It produces small, firm, dome-shaped bumps with a characteristic dimple (umbilication) in the center. While harmless and self-limiting, it can persist for months to years and spread easily between children.

MRSA is a type of Staphylococcus aureus bacteria that has developed resistance to methicillin and many commonly used antibiotics. In babies and children, MRSA most often causes skin and soft tissue infections, including boils (furuncles), abscesses, and infected wounds. Community-acquired MRSA (CA-MRSA) has become increasingly common in otherwise healthy children who have no healthcare exposure, while hospital-acquired MRSA (HA-MRSA) occurs in infants in NICUs or after surgical procedures.

Ringworm is a common fungal skin infection that has nothing to do with worms. It causes a ring-shaped, red, scaly rash with a clear center and raised edges. In children, it can affect the body (tinea corporis), scalp (tinea capitis), or feet (tinea pedis).

Scabies is a highly contagious skin infestation caused by the microscopic mite Sarcoptes scabiei. The mites burrow into the skin and lay eggs, causing intense itching and a pimple-like rash. In babies, the presentation differs from older children and adults, often affecting the palms, soles, head, and face.

Staphylococcal (staph) skin infections are caused by Staphylococcus aureus bacteria, one of the most common bacteria found on human skin. While many people carry staph harmlessly on their skin or in their nose, it can cause a range of skin infections when it enters through a break in the skin. In babies and young children, staph causes boils (furuncles), folliculitis, wound infections, and is a primary cause of impetigo and cellulitis. Most staph skin infections are treatable with standard antibiotics.

Warts are benign skin growths caused by human papillomavirus (HPV). While uncommon in infants, they become more frequent in toddlers and young children. Common warts (verruca vulgaris) appear as rough, raised bumps most often on the hands and fingers. Plantar warts (verruca plantaris) grow on the soles of the feet and can cause discomfort with walking. Flat warts (verruca plana) are smooth, small, and tend to appear in clusters. Most warts in children are harmless and resolve on their own within 1-2 years as the immune system clears the virus.

Bacterial meningitis is a serious, life-threatening infection of the membranes (meninges) surrounding the brain and spinal cord. In infants and young children, the most common causes are Group B Streptococcus (newborns), Streptococcus pneumoniae, and Neisseria meningitidis. Early recognition and treatment are critical as the disease can progress rapidly and cause death or permanent disability within hours.

Group B Streptococcus (GBS, Streptococcus agalactiae) is a leading cause of serious bacterial infection in newborns. Approximately 25% of pregnant women carry GBS in the vaginal or rectal area without symptoms. During birth, bacteria can be transmitted to the baby, causing early-onset disease (within the first 7 days of life, usually within 24-48 hours) or late-onset disease (7 days to 3 months of age). GBS can cause sepsis, pneumonia, and meningitis. Universal maternal screening and intrapartum antibiotic prophylaxis have dramatically reduced early-onset disease.

Henoch-Schönlein Purpura (HSP), now formally called IgA vasculitis, is the most common vasculitis in children. It is characterized by inflammation of small blood vessels (small-vessel vasculitis) caused by deposition of IgA immune complexes. The classic tetrad includes palpable purpura (non-blanching rash predominantly on the legs and buttocks), arthritis or joint pain, abdominal pain, and kidney involvement (nephritis). HSP most commonly affects children aged 3-10 years and often follows an upper respiratory infection. While usually self-limited, kidney involvement requires monitoring as it can occasionally cause long-term damage.

Invasive Group A Streptococcal (iGAS) disease occurs when Group A Streptococcus (Streptococcus pyogenes) bacteria invade normally sterile body sites such as the blood, muscles, lungs, or cerebrospinal fluid. While Group A Strep commonly causes mild infections like strep throat and impetigo, invasive disease is rare but life-threatening. Manifestations include necrotizing fasciitis ("flesh-eating disease"), streptococcal toxic shock syndrome (STSS), bacteremia, pneumonia, and deep tissue infections. Pediatric cases have increased in recent years, particularly following the COVID-19 pandemic, raising significant public health concern.

Immune Thrombocytopenic Purpura (ITP) is an autoimmune bleeding disorder where the immune system mistakenly destroys platelets, leading to a low platelet count (thrombocytopenia). In children, ITP most commonly occurs between ages 2-6 and frequently follows a viral illness or vaccination by 1-4 weeks. Unlike adult ITP, childhood ITP is usually acute and self-limited, with approximately 80% of children recovering within 6-12 months regardless of treatment. The primary clinical concern is bleeding, which ranges from mild bruising and petechiae to rare but serious intracranial hemorrhage.

Kawasaki disease is an acute inflammatory condition that primarily affects children under 5. It causes inflammation of blood vessels (vasculitis) throughout the body, with particular danger to the coronary arteries of the heart. The cause is unknown but likely involves an abnormal immune response to an infectious trigger in genetically susceptible children. Early diagnosis and treatment with IVIG can prevent serious heart complications.

MIS-C is a rare but serious condition where different body parts become inflamed, including the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs. It typically occurs 2-6 weeks after a SARS-CoV-2 (COVID-19) infection, even if the child was asymptomatic during the initial infection. It shares features with Kawasaki disease and toxic shock syndrome but is a distinct entity.

Necrotizing enterocolitis (NEC) is a devastating intestinal disease that primarily affects premature infants, occurring when the lining of the intestinal wall dies and the tissue separates from the wall (necrosis). It is the most common and most serious gastrointestinal emergency in neonates. NEC affects approximately 5-12% of very low birth weight infants (<1500g) and has a mortality rate of 20-30%. The pathogenesis involves an immature intestinal barrier, abnormal bacterial colonization, ischemia, and an exaggerated inflammatory response. Human breast milk is strongly protective against NEC.

Neonatal sepsis is a serious bloodstream infection occurring in infants within the first 28 days of life. It is classified as early-onset (EOS, within 72 hours of birth) or late-onset (LOS, after 72 hours to 28 days). Early-onset sepsis is primarily caused by organisms acquired from the maternal genital tract during labor and delivery, with Group B Streptococcus (GBS) and Escherichia coli being the most common pathogens. Late-onset sepsis may be acquired from the birth canal, hospital environment (nosocomial), or community. Neonatal sepsis remains a leading cause of morbidity and mortality in newborns, particularly premature infants, and symptoms are often subtle and non-specific, making a high index of clinical suspicion essential.

Sepsis is a life-threatening condition where the body's response to an infection causes widespread inflammation and organ dysfunction. In infants and children, sepsis can progress rapidly from a seemingly mild infection to septic shock and multi-organ failure within hours. It is the leading cause of death from infection in children. Early recognition and aggressive treatment are critical for survival.

Viral meningitis is an inflammation of the membranes (meninges) surrounding the brain and spinal cord caused by a viral infection. Enteroviruses (coxsackievirus, echovirus) are the most common cause, accounting for approximately 85% of cases. While still a serious condition requiring medical evaluation, viral meningitis is generally less severe than bacterial meningitis and most children recover fully within 7-10 days. However, neonates and immunocompromised children are at higher risk for severe disease.

Eczema (atopic dermatitis) is a chronic, relapsing inflammatory skin condition that affects up to 20% of children. It causes dry, itchy, red, and inflamed patches of skin. It typically begins in infancy (60% develop it in the first year) and is part of the "atopic triad" along with asthma and allergic rhinitis. While there is no cure, proper management can control symptoms effectively.

Food allergies occur when the immune system mistakenly identifies a food protein as harmful and mounts an immune response. They affect approximately 8% of children. The top 9 allergens (milk, egg, peanut, tree nuts, wheat, soy, fish, shellfish, sesame) account for most reactions. Reactions range from mild hives to life-threatening anaphylaxis. Early introduction of allergenic foods may prevent food allergy development.

GERD is a condition where stomach contents frequently flow back into the esophagus, causing troublesome symptoms or complications. While simple reflux (GER) is normal in infants — affecting up to 70% of 4-month-olds — GERD is diagnosed when reflux causes significant symptoms like poor weight gain, feeding refusal, esophagitis, or respiratory problems. Most infant reflux resolves by 12-18 months as the lower esophageal sphincter matures.

Iron deficiency anemia is the most common nutritional deficiency in young children worldwide, affecting approximately 8% of toddlers in the United States. It occurs when the body does not have enough iron to produce adequate hemoglobin, the protein in red blood cells that carries oxygen. In young children, it can impair cognitive development, motor skills, and behavior. Prevention through adequate iron intake is critical during the rapid growth of infancy and toddlerhood.

Hydronephrosis is the swelling (dilation) of the kidney due to buildup of urine, caused by obstruction or reflux. It is the most common abnormality detected on prenatal ultrasound, found in 1-5% of all pregnancies. Most cases are mild and resolve spontaneously without intervention. Causes include ureteropelvic junction (UPJ) obstruction, vesicoureteral reflux, posterior urethral valves (boys), and ureterovesical junction obstruction. The severity is graded by the degree of renal pelvis dilation.

Pyelonephritis is a bacterial infection of the kidney, representing the most serious form of urinary tract infection in children. It occurs when bacteria (usually E. coli) ascend from the bladder to the kidneys. It is particularly concerning in young children because it can cause permanent renal scarring, which may lead to hypertension and chronic kidney disease. Prompt diagnosis and adequate antibiotic treatment are critical to preventing long-term kidney damage.

A urinary tract infection (UTI) is a bacterial infection of the urinary system (kidneys, ureters, bladder, or urethra). UTIs are one of the most common bacterial infections in children, affecting about 8% of girls and 2% of boys by age 7. In young infants, UTI is an important cause of unexplained fever. E. coli causes 80-90% of pediatric UTIs. Prompt diagnosis and treatment are essential to prevent kidney damage, especially in young children.

Vesicoureteral reflux (VUR) is a condition where urine flows backward from the bladder into the ureters and potentially into the kidneys. It is the most common urological abnormality in children, affecting approximately 1-2% of all children and found in 30-40% of children who present with a UTI. VUR is graded I through V based on severity. The primary concern is that reflux of infected urine into the kidneys can cause renal scarring and long-term kidney damage. Many children with low-grade VUR outgrow it as the bladder matures.

Chickenpox is a highly contagious viral illness caused by the varicella-zoster virus (VZV). It causes an itchy, blister-like rash covering the body along with fever and fatigue. Thanks to vaccination, chickenpox is much less common than it once was, but it still occurs in unvaccinated or partially vaccinated children. It is more serious in infants under 1 year who are too young to be vaccinated.

Hand, foot, and mouth disease (HFMD) is a common, highly contagious viral illness primarily caused by Coxsackievirus A16 and Enterovirus 71. It causes painful sores in the mouth and a characteristic rash with blisters on the hands, feet, and sometimes the buttocks and legs. It is most common in children under 5, with outbreaks peaking in summer and early fall. HFMD is generally mild and self-limiting but can cause significant discomfort.

Fifth disease is a mild viral illness caused by Parvovirus B19. It is called "fifth disease" because it was the fifth in a historical list of common childhood rash illnesses. Its hallmark is a bright red "slapped cheek" rash on the face, followed by a lacy rash on the body. Most children feel well once the rash appears. It is most common in school-age children but can affect toddlers.

Herpangina is a common viral illness in children caused by enteroviruses, most often Coxsackievirus Group A. It causes sudden high fever and painful blister-like ulcers in the back of the throat and soft palate. Unlike hand-foot-and-mouth disease (which is caused by related viruses), herpangina lesions are confined to the mouth and throat. It is most common in summer and fall and peaks in children aged 3-10 years.

Measles is a highly contagious viral illness caused by the measles virus (a paramyxovirus). It causes a distinctive red blotchy rash, high fever, cough, runny nose, and conjunctivitis. Before vaccination, measles infected 3-4 million Americans annually. While now rare in the US due to MMR vaccine, outbreaks still occur in unvaccinated communities. Measles remains a leading cause of childhood death globally, killing over 100,000 children per year worldwide.

Roseola is a very common viral illness caused by Human Herpesvirus 6 (HHV-6) or sometimes HHV-7. It is characterized by 3-5 days of high fever followed by a distinctive pink rash that appears as the fever breaks. Nearly all children get roseola by age 2, and most cases occur between 6 months and 2 years of age. The rash appearance is actually a sign that the illness is resolving.

Scarlet fever is a bacterial illness caused by Group A Streptococcus (GAS) that produces a characteristic red, sandpaper-textured rash. It typically occurs alongside strep throat or occasionally strep skin infections. Most common in children ages 5-15, it was once a serious childhood disease but is now easily treatable with antibiotics. The rash is caused by erythrogenic toxins produced by the bacteria.

A viral exanthem is a widespread rash that occurs as part of a viral infection. Many different viruses can cause rashes in children, and often the specific virus is never identified. These rashes are extremely common in young children — most children will have multiple viral rashes before age 5. Common causes include adenovirus, enterovirus, HHV-6 (roseola), parvovirus B19 (fifth disease), and many others. Most viral exanthems are harmless and self-limiting.