KANSAS CITY — The frozen pizza category is piping hot.

In the 52 weeks ended Sept. 9, dollar sales in the frozen pizza category totaled $4,890,882,560, up 4.5% from the same period a year ago, while unit sales increased nearly 3% to 1,354,621,824, according to Information Resources, Inc., a Chicago-based market research firm.

Three of the nation’s four largest frozen pizza makers posted year-over-year dollar sales gains during the past year, led by a 4.6% increase at Schwan Food Co., Marshall, Minn. Meanwhile, dollar sales at Minneapolis-based General Mills, Inc. increased 2.3%, and dollar sales at category leader Nestle USA, Inc., Arlington, Va., rose 0.9%, according to I.R.I.

But the biggest market mover during the 52-week period was private label. Dollar sales of private label frozen pizzas increased 11.3% to $649,487,232 on a 15.7% increase in unit sales.

Even as private label charged up the charts, four of the top five frozen pizza brands managed to post year-over-year dollar sales gains. DiGiorno, Nestle’s top selling brand and the category’s top selling brand overall, posted dollar sales of $1,105,476,352 in the 52 weeks ended Sept. 9, up 3.1% from the same period a year ago. Dollar sales for Red Baron, the top selling brand of Schwan Food, rose 7% to $614,249,024. General Mills’ top selling brand, Totino’s Party Pizza, also registered a year-over-year gain, climbing 2.8% to $368,059,840.

With the major frozen pizza brands experiencing solid growth over the past year it may appear that there was little room for new entrants in the category, but just the opposite rang true.

Nestle in September 2017 acquired Sweet Earth, a plant-based foods manufacturer based in Moss Landing, Calif. The acquisition gave the company an immediate entry into the plant-based foods segment. In June, Nestle and Sweet Earth combined their expertise to put a plant-based spin on pizza.

Available in Veggie Lover’s, Truffle Lover’s, Protein Lover’s and Herb Lover’s varieties, each Sweet Earth frozen pizza contains at least 5 grams of fiber per serving and features crusts blended with ancient grains, carrot and rosemary.

“We believe food should be delicious, but it should also make you feel good past the moment you’re eating it,” said Kelly Swette, chief executive officer of Sweet Earth Foods. “Our new pizzas are chock-full of fresh ingredients that provide exceptional taste and nutrition, with the convenience that comes in the freezer aisle.”

Brian Swette, president of Sweet Earth Foods, added, “Plant-based eating is good for the planet and good for you. Sustainability is at the core of everything we do, beginning with the ingredients we use. Our customers are looking to add more vegetables and plant-based protein to their diet, and we are continuing to serve and empower them with our new line of frozen pizzas.”

Around the same time as the launch of the Sweet Earth pizza brand Nestle said it has invested in Outsiders Pizza Co., which is part of Foundry Foods, an innovation incubator backed by Nestle USA. Outsiders offers frozen pizza based on regional styles such as Detroit and Milwaukee.

In mid-August, it was announced that a line of frozen pizzas is launching as part of an ongoing collaboration between the Kraft Heinz Co. and Oprah Winfrey. O, That’s Good! Frozen Pizza is the third product category from Mealtime Stories, L.L.C., the joint venture between Kraft Heinz and Ms. Winfrey, which last year unveiled refrigerated soups and side dishes with a better-for-you twist.

Featuring a crust made with cauliflower, varieties include pepperoni, five cheese, supreme and fire roasted vegetable.

“At Kraft Heinz, we understand that the trifecta of great taste, real ingredients and convenience in food options is nearly impossible to find,” said Christopher Urban, head of Mealtime Stories at Kraft Heinz. “After the success of O, That’s Good! refrigerated soups and sides, we wanted to bring excitement to the pizza category and give families even more delicious options to please everyone at the dinner table.”

Caulipower, Los Angeles, in March took its frozen pizza brand beyond the United States to Canada with the launch of four better-for-you pizzas: Margherita, three-Cheese, veggie and plain crust. The frozen pizza line featuring a cauliflower-based crust debuted in the United States in 2017 and has gone from distribution in 60 stores to more than 8,000 stores in a year’s time, the company said.

Cauliflower also is at the center of a new product introduced by B&G Foods, Inc., Parsippany, N.J. Green Giant Cauliflower Pizza Crust is offered in original and Tuscan varieties.

“Think about products that are made from vegetables, which could go after different places in the frozen food case, like pizza crust,” Kenneth G. Romanzi, executive vice-president and chief operating officer of B&G Foods, said during a Sept. 5 presentation at the Barclays Global Consumer Staples Conference in Boston.