In 2005, the consumer products giant Colgate-Palmolive left the North American laundry detergent business by selling products such as Fab and Dynamo to Phoenix Brands. Three years later, another consumer goods powerhouse, Unilever, sold its U.S. detergents lineup, including All and Wisk, to Sun Products.

The sales of the businesses to two smaller, privately owned companies left Procter & Gamble virtually unchallenged in the premium segment of the U.S. laundry detergent market. P&G, interestingly, did not declare victory.

Indeed, in 2014, P&G’s then-chief executive officer, Alan G. Lafley, lamented Unilever’s exit. He said it hollowed out the middle of the detergents market, pitting P&G, with products mostly at the high end, against three competitors with low-tier offerings. A marketer of well-known brands such as Tide and Gain, P&G commanded almost 60% of the U.S. laundry detergent business, but it was a stagnating business with a dangerous price gap between the company’s products and those of its rivals.

A year later, one of those competitors, the German company Henkel, shook things up. It brought Persil, its premium European detergent, to the U.S., first selling it exclusively through Walmart, then later launching it at retailers such as Target. In 2016, Henkel mixed things up further by acquiring Sun Products.

The launch of Persil reinvigorated the laundry detergent business, but perhaps more quickly than Lafley had expected. He and other P&G executives must have been stunned last May when Consumer Reports magazine ranked one of the new Henkel products, Persil ProClean Power-Liquid 2in1, as the best-performing U.S. laundry detergent. The coronation pushed Tide into the number two slot for the first time in many years.

Chastened, P&G reformulated its former number one variety, Tide Ultra Stain Release, in 2016. The company says it added a surfactant and removed some water, creating a denser, more concentrated formula that offers improved stain removal. The product retook the top spot in a follow-up Consumer Reports analysis, although by a statistically insignificant thread, the magazine says.

It’s too early to say whether Henkel will seriously challenge P&G for U.S. consumers who buy high-end laundry detergents. But if P&G’s formulation chemists felt any complacency owing to lack of competition, they surely have been jarred out of it.

In the U.S., Tide and Persil are premium products in a business that can be divided into four performance tiers, explains Shoaib Arif, manager of applications and technical service at Pilot Chemical, a surfactants supplier. Over the years, Arif and other Pilot scientists have helped many household goods companies formulate new detergents and other cleaning products.

At the low end are ultra-economy detergents, which according to Arif may contain little more than an inexpensive surfactant such as linear alkylbenzene sulfonate (LABS) plus fragrance and color. Products on the next tier might add a surfactant aid, or builder, such as sodium citrate, a viscosity enhancer, and a second surfactant.

LABS is an anionic surfactant that excels at removing particulate matter from fabric and works well on cotton. A common second surfactant is alcohol ethoxylate, a nonionic that is more effective than LABS at removing greasy soils, particularly from synthetic fibers.

On the third tier, at a price point just below premium, a formulator might add optical brighteners, which make clothes appear brighter by absorbing ultraviolet light and reemitting it in the blue region. Also often found in such formulas are better surfactants, chelating agents, additional builders, and antiredeposition polymers that capture soil from the wash water to keep it from redepositing on fabrics.

The most expensive detergents are characterized by high surfactant loading and a multiplicity of additional surfactants such as alcohol sulfates, alcohol ethoxysulfates, amine oxides, fatty acid soaps, and cationics. Exotic soil-capturing polymers—some that are custom-made for companies such as P&G and Henkel—and enzymes are also in such formulas.

Piling on ingredients, though, brings its own challenges, Arif cautions. Detergent formulation is a science to the extent that chemists know the qualities of individual ingredients, such as the surface-active properties of a surfactant.

“But once you formulate, then all these things interact with each other and you can’t predict exactly what the final formula will do,” he explains. “You still have to test to make sure it works in real life.”

Enzyme activity, for example, can be inhibited by surfactants and builders, Arif says. Detergent formulators counter this problem with enzyme stabilizers such as sodium borate and calcium formate.

The high surfactant loading found in premium detergent brands can also create problems, points out Franco Pala, principal research scientist in Battelle’s World Detergent Program. “It’s not simple to add so many surfactants at such a high concentration,” Pala explains. Solubility becomes a problem, as are unwanted interactions between surfactants.

Started in the early 1990s, the multiclient Battelle program that Pala leads analyzes the composition of major cleaning product brands around the world. Using a battery of scientific instruments, Battelle helps brand owners and raw material suppliers go beyond the ingredients list to learn, for example, the degree of ethoxylation of a surfactant or whether surfactant backbones are linear or branched.

These days, Pala says, polymers are a big source of innovation in detergent ingredients. Both the Tide and Persil products, for example, contain polyethyleneimine ethoxylate, a soil-capturing and -releasing polymer that was developed by BASF for P&G but is now being offered to detergent makers more broadly.

Also found in some premium detergents, Pala notes, are copolymers of terephthalic acid that coat fabrics during the wash to ease removal of stains and soils in subsequent washing. Battelle uses tools such as gel permeation chromatography to isolate polymers and then infrared spectrometry to determine their structure.

The Battelle program also pays close attention to enzymes, products of biotechnology that manufacturers continue to improve on an annual basis. To assess enzyme activity, Pala’s team exposes enzymes to a substrate containing a chromophore. When the enzyme degrades the substrate, the chromophore is released and measured by absorption or fluorescent spectrometry.

Protein-attacking proteases were the first enzymes to be added to detergents, in the late 1960s. Later additions to the enzyme arsenal include amylases, which break down starches, and mannanases, which degrade the thickening agent guar gum. When guar-containing foods such as ice cream and barbecue sauce spill on clothing, the gum can remain behind, even after washing. Embedded in the fabric, it acts like glue for particulate soils, creating hard-to-remove stains.

Both Persil ProClean Power-Liquid 2in1 and Tide Ultra Stain Release contain protease, amylase, and mannanase.

Persil also contains lipase, which breaks down fat, and cellulase, which cleans indirectly by hydrolyzing certain glycosidic bonds in cotton fibers, thus removing soils attached to the fibers. Cellulase also softens cotton and improves its color brightness. Unique to the Tide detergent, meanwhile, is glucanase, which breaks down polysaccharides that amylase doesn’t, according to patent literature.

Novozymes and DuPont have long been the big enzyme manufacturers, but BASF recently entered the business with a protease. At a cleaning products conference in Germany last fall, BASF promoted a combination of its new protease with polyethyleneimine ethoxylate, saying the blend offers enhanced performance for customers that want to formulate detergents for low-temperature washing.

Indeed, Arif and other market watchers say ingredients that allow detergent makers to make environmental claims about low energy consumption or natural origins are a next frontier for the industry. In May of last year, P&G launched Tide Purclean, a version of its signature brand in which 65% of the ingredients are plant-derived. Then in October Unilever reentered the U.S. detergents market when it acquired Seventh Generation, a maker of plant-derived detergents and other cleaning products.

Although turning the best ingredients into award-winning detergents will always be a challenge, “the trend today is more natural,” Arif says. “Customers are asking, ‘How do we make products that are naturally derived and less toxic to humans and the environment, but still perform as well?’ ”