Photos of mamas breastfeeding [1] their babies and even their friend's child [2] have gone viral, with many attempting to create a positive dialogue around this topic. A new study, however, may put a damper on this discussion.

The research, published in Environmental Science & Technology [3], shows that the longer a baby is breastfed — known as extended breastfeeding [4] — the greater that baby's exposure is to a class of industrial chemicals. These chemicals are called perfluorinated alkylate substances (PFASs) and are found in things like clothing or food packaging to make them resistant to water, grease, and stains.

In a small study with 81 babies born between 1997 and 2000, researchers found that exclusively breastfed babies had high concentrations of PFAS (researchers looked at the baby's blood samples over time to determine this), which rose roughly 20 to 30 percent for each month of breastfeeding. When mothers stopped breastfeeding their children, PFAS levels went down.

PFASs have been linked to problems with the immune, reproductive, and endocrine systems — and even cancer.

An important point to note, however, is that PFASs are known to be in breast milk already.

While there is no reason to discourage breastfeeding, the author Philippe Grandjean said, "We are concerned that these pollutants are transferred to the next generation at a very vulnerable age. The current US legislation does not require any testing of chemical substances like PFASs for their transfer to babies and any related adverse effects."