One theory is that gastroesophageal reflux disorder (GERD) causes colic, but there is inconsistent evidence for this, and treatments for GERD are ineffective for reducing colic.[1][2][3]
Hypersensitivity to cow’s milk, lactose intolerance, and reactions to allergens in breast milk from the mothers diet may be responsible for colic in some infants. This follows from the observation that exclusive use of hypoallergenic formula and/or maternal elimination diets may benefit colic in some cases. However, evidence for this is inconsistent.[4][5][6][7][8][3][9] The evidence that these factors contribute to colic is stronger where there are atopic conditions present, such as eczema or psoriasis, and when symptoms of colic start after the first month of life.[4]
Immature synthesis and malabsorption of bile acids (which help to digest and absorb fats) may lead to the presence of fats and other nutrients in the large intestine. This may contribute to colic by influencing the bacteria in the large intestine consuming these nutrients and producing gas.[10]