Many different types of milk (other than an infant formula) have been given to babies in the past, but we now know that a lot of these are not suitable for babies and can cause serious health problems.

The base in the majority of infant formulas comes from cow’s milk, goat’s milk or soy beans, which has been modified or changed with important nutrients added so that the formula is similar to breast milk in nutrient composition.

It’s not a perfect match because the exact chemical make-up of breast milk is unknown.

The Food and Drug Administration is telling parents, health care workers and people who take care of babies to avoid using a thickener for breast milk or formula fed to premature infants.

A product called SimplyThick may be causing life-threatening damage to children’s intestines, the agency said.

The FDA, which first learned about possible problems with SimplyThick on May 13, is now aware of 15 cases of necrotizing enterocolitis (NEC), including two deaths.

In all those cases, the FDA says SimplyThick gel was added to the formula or breast milk fed to the babies, who had trouble swallowing because of complications from their premature birth.