Be careful while purchasing breast milk online. It may be contaminated, researchers of a new study warn.

The World Health Organization recommends feeding a new born baby breast milk, at least till the baby is six months old. Many parents often opt to buy breast milk online. A study conducted by the Research Institute at Nationwide Children's Hospital in Columbus found that three-fourths of such milk sold on the Internet is contaminated with bacteria.

"If you buy milk on the internet, you have no idea what you're getting," said Sarah Keim, the study lead. "A buyer would just have no way of being able to know with the information they have whether that milk is safe."

101 milk samples bought online were tested and researchers found that a majority of them were not safe enough for children, especially not premature infants.

Over the years, Keim and her colleagues noticed a boom in the number of websites selling breast milk. These websites have thousands of advertisements offering milk from new mothers who make extra milk. The typical price ranges between $1 and $2 per ounce. After replying to over 495 such ads, researchers collected the 101 samples for the study.

Seventy-four per cent of the samples either had disease-causing bacteria like E coli or harmful levels of bacteria such as Streptococci. Keim didn't clarify whether the contaminated milk would guaranteed make babies sick but deemed it unsafe, especially for preemies and infants that have higher than average risks for medical problems. The milk can be even more dangerous when fed to infants raw.

It is not uncommon for breast milk to have bacteria and Keim confirmed that breast milk is contaminated with different forms of bacteria even before it comes out of the breast. These bacteria help strengthen a baby's digestive and immune system. However, bacteria found in online breast milk is not the "good type." Though none of samples tested positive for HIV, one in five samples contained traces of cytomegalovirus, a bacteria that can cause serious health issues for infants with weak immune systems.

According to a Reuters Health report, one website selling breast milk has already taken note of the problem and officials confirmed they're working on a solution.

"We have made the decision to transition away from offering breast milk classified ads and in the near future completely remove them with the goal (of stopping) all...activities related to informal milk sharing," Onlythebreast.com administrators said in a statement.

"We are convinced that a more safety centered approach must be taken to secure milk sharing. After careful consideration, we will be shifting our focus from mother to mother internet sales to helping qualified Only the Breast donors provide milk to a new milk banking program."