When a parent puts a bottle of baby formula to a child's lips, the parent might not know exactly what ingredients are in that thick, nutritionally packed mix. But rocket fuel? That's not an ingredient many expect to find.
A study by government researchers released Thursday tested 15 different brands of formula and found a chemical -- also found in rocket fuel -- contaminating every single one.
While the levels of the chemical, perchlorate, have been deemed safe by the Environmental Protection Agency, some worry public health is at risk.
Scientists at the Centers for Disease Control and Prevention tested the formula for the presence of perchlorate, a chemical used as the main ingredient in solid rocket fuel. It's a worry because perchlorate can interfere with the production of thyroid hormones by inhibiting the absorption of iodine.
The CDC study found cow's milk-based formula contained more perchlorate than that made with soy or other ingredients.
The two brands with the highest levels -- more than double that of the other milk-based products -- command 87 percent of the market share for infant formula.
The report does not specify the brand names of any formula tested.
Perchlorate has been found in the water supplies of 35 states and has been detected in everything from vegetables to milk. In the case of dairy, the rocket fuel in the water flows into grass, which is eaten by cows, and is then passed along into milk.
The perchlorate was found in levels within a range that's been deemed safe by the Environmental Protection Agency.
CDC researchers write that "this is reasssuring at first glance," but add that it could be problematic because drinking water in 26 states has high perchlorate levels. So, mixing contaminated powdered milk with contaminated water in those places could result in a dangerous exposure.
"The widespread penetrance of these products, and the potential for utilization of water for reconstitution that has even minimal concentrations of perchlorate," the researchers write, "suggest that a significant number of infants consuming bovine milk-based [powdered infant formula] with lactose, will have perchlorate doses in excess of the [recommended limit]."
The Environmental Working Group, an organization that advocates for stricter limits on a variety of chemicals, contends EPA's recommended limit is set "too high to protect public health" and understates the risk.
"Perchlorate contamination of drinking water is a very serious concern, particularly for infants," said Dr. Anila Jacob, an Environmental Working Group scientist.
Dr. Sheela Sathyanarayana, a pediatrician who works on environmental health issues at Seattle Children's Hospital and at the University of Washington department of pediatrics, said it's difficult to say whether this sort of exposure is dangerous.
"Considered in isolation, these perchlorate concentrations in formula are not concerning for child health," Sathyanarayana wrote in an e-mail to ABC News. "The reason that some may be concerned about health effects to children is that there are several sources of perchlorate in our environment ... and, therefore, the cumulative dose of perchlorate to an infant may be much higher than that found in the formula."