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Parents have been warned to check the temperature of babies' formula as a recent study showed 85% of machines tested did not kill harmful bacteria.
A mum who took part in the study said she was "shocked" to see her preparation machine failed despite being made specifically for babies.
Formula-fed babies have a higher risk of infections due to bacteria that live within powdered infant formula.
Researchers want better formula labelling and more data collection.Swansea University's study revealed 85% of the 74 infant formula preparation machines tested by parents in UK homes did not produce water hot enough to kill harmful bacteria in infant formula.
This was compared with 69 parents in the study who used a kettle to heat the water, where 22% reported water temperatures not sufficiently hot enough.
Jonie Cooper, a parent who took part in the study, said the first time she tested her machine's water it was only 52C.
"When I saw this I was shocked because I trusted the machine to follow the NHS guidelines on the temperature of the water, because it was specifically designed for babies.