In children, obesity is defined as a body mass index (BMI) greater than the 95th percentile for age and sex. Severe obesity is defined as a BMI in the 99th percentile, or over 120% of the 95th percentile value, or a BMI greater than 35 (weight in kilograms divided by height in meters squared). BMI reference standards for children ages 2-20 are published by the US Centers for Disease Control and Prevention (CDC) and the US National Center for Health Statistics (NCHS).

Pediatric obesity increases in prevalence with age. In the United States, approximately 14% of preschool children and 21% of adolescents are obese. Severe obesity also increases in prevalence with age. Approximately 2% of preschool children and 7%-10% of adolescents are severely obese. Risk factors include ethnicity (Native American, African American, and Mexican American patients are at increased risk), low socioeconomic class, low education level, and living in a rural community. In the United States, childhood obesity rates have been rising for the last several decades. Obesity tends to persist into adulthood.

The majority of obese children are obese due to a net-positive energy balance resulting from high caloric intake and insufficient physical activity.

There are many risk factors for the development of pediatric obesity. In rare instances, a specific genetic, hypothalamic, or endocrine disorder will predispose a patient to obesity. Specific mutations in GNAS and their effects on G protein-coupled receptor (GPCR) signaling have been identified. Rare cases of early-onset obesity are associated with variants in leptin. More often, environmental factors such as high consumption of sugar-rich beverages, physical inactivity, and excess screen time all contribute to a net-positive caloric balance that leads to obesity. The role of epigenetics in obesity is an emerging field of research for which specific causality has yet to be defined.

The following common skin conditions are seen more frequently in obese pediatric patients: hyperhidrosis and bromhidrosis, bacterial and candidal skin infections, onychomycosis, acne vulgaris, hirsutism, hidradenitis suppurativa, psoriasis, and rosacea.

Additionally, obese pediatric patients have an increased risk of psychosocial conditions such as depression and eating disorders; cardiovascular conditions such as hypertension, dyslipidemia, and coagulopathy; gastrointestinal conditions such as gallstones and nonalcoholic fatty liver disease; endocrine conditions such as diabetes mellitus type 2, precocious puberty, polycystic ovary syndrome, and male hypogonadism; pulmonary conditions such as asthma and sleep apnea; and renal conditions such as glomerulopathy. Childhood obesity has been shown to increase risk for adult cardiovascular events, including death, before the age of 60.