Asda and Tesco have joined Sainsbury's and Iceland in reducing the cost of Aptamil baby formula.
Asda also said it will let customers pay for baby formula using their rewards scheme vouchers for the first time.
It comes amid a Competition and Markets Authority (CMA) investigation into formula products over fears they are particularly vulnerable to price shocks.
The CMA found a 25% uplift in price over two years.
Producers of baby formula have all blamed higher factory costs, including ingredients and energy.
But last week Iceland said it would be cutting the cost of Aptamil from 16 January after manufacturer Danone, which also makes the Cow & Gate brand, agreed to reduce the price at which it offers its Aptamil powdered formula to retailers by up to 7%. Sainsbury's also reduced the price of some branded baby formula by 7%.
Asda said it would cut the price of six Aptamil lines "the majority by an average of 7%".
Tesco said it was to cut the price of five Aptamil products by between 80p and £1 from Tuesday.
Asda's chief commercial officer, Kris Comerford, said: "For many of Asda's customers, and families nationwide, we understand that buying baby formula is a vital necessity in their weekly shop, which is why we're taking swift action to pass on falling manufacturing costs to customers before any other retailer.
"At the same time, we've decided to remove exclusions on using Asda rewards vouchers to pay for baby formula as we want to do everything we can to help families manage their budget and keep their family fed."