French food giant Danone is looking into reports that its Aptamil baby milk formula is making some infants ill.
Aptamil recently changed the recipe of three of its baby milk formulas.
Hundreds of parents in the UK have complained on social media that the revised formula milk is making their babies sick.
Danone said it had carried out extensive safety checks, but added that it was "taking all feedback very seriously".
The food giant said it was now investigating the complaints and had set up a free dedicated one-to-one helpline where parents can call for advice.
Parents in the UK are advised to call 0800 996 1000, pressing option 0 followed by option 1.
'Smelled different'
Several mothers have told the BBC that their babies have experienced upset stomachs after they started using the new version of Aptamil First Infant Milk powder (stage 1).
The parents said they noticed that the milk powder did not dissolve in the milk bottles, leaving clumps of residue.
"It smelled different, like gone-off milk that had been left out for a day," Rosie Menzies from Lymington, Hampshire told the BBC.
Ms Menzies said that her 11-week-old son Harry would be sick soon after feeds and began to refuse bottles, until she started using a different formula by another brand.
Danone UK said: "We would like to reassure parents that the quality and safety of our products is our number one priority. We have recently introduced new Aptamil formulations and we recognise that some families have not found the transition to the new formula easy.
"We have undertaken extensive quality and safety checks, including clinical trials, product testing and product experience tests on these products. The results have shown that babies take to this formula well and that it is safe.
"We have updated the mixing instructions on our packs as this new formula requires parents to mix it up slightly differently, compared to the previous formulation - specifically, shaking vigorously for 10 seconds to dissolve the powder."
Aptamil told customers on its Facebook page that it had changed the recipes of three products: Aptamil First Infant Milk powder (stage 1), Aptamil Follow On Milk powder (stage 2), Aptamil Growing Up Milk powders (stages 3 & 4).
The rest of its products remain unchanged.
