Some cheap baby feeding bottles sold in New Zealand have inaccurate markings, meaning some babies could be getting infant formula that is too concentrated, the Ministry of Health says.
Consumer Affairs, part of the Ministry of Business, Innovation and Employment, has surveyed volume indicator markings on 35 bottles.
It found that 15 bottles had volume markings that were inaccurate by more than five percent, and these bottles tended to be purchased from discount shops.
Formula that is too concentrated can cause babies to experience vomiting, diarrhoea and constipation and left untreated, this can cause serious dehydration.
Over time, formula that is too concentrated will provide excess energy and other nutrients, which could lead to overweight or obese babies and toddlers.
It could also harm organs such as the kidneys, when they are still immature, the Ministry of Health says.
Most feeding bottles are imported and some meet a European regulatory standard that means the bottles are accurate.
However, these bottles can be more expensive than bottles sold at discount shops.
Caregivers using infant formula are being advised to get the accuracy of their feeding bottles checked at a pharmacy.