In the first six months of life, infants are particularly prone to gastrointestinal (GI) signs and symptoms that have no obvious structural or biomechanical cause. The immature GI tract and its associated nervous system and microbiota are not yet functioning at optimal level. This can cause a range of disorders that are not classified as organic disease, but which can nevertheless be extremely distressing for both the infant and the concerned parents. The collective term for these conditions is functional GI disorders. Around 50% of infants will suffer at least one functional GI disorders before six months of age. The most common one is reflux (which affects around 30% of infants), followed by colic (around 20% of infants) and constipation (around 15%). It is common for two or more functional GI disorders to coexist in the same infant. Learn more about common infant feeding problems below.