In less than four years, the Honest Company Inc. surged to a $1.7 billion private valuation thanks to its marketing of cleaning supplies, diapers and other consumer products that it says are safer and more ecologically friendly than other brands.

The company, co-founded by actress Jessica Alba, is challenging giants such as Procter & Gamble Co. and Clorox Co. with a guarantee that its offerings don’t contain what it says are harsh chemicals found in many mainstream products. One of the primary ingredients Honest tells consumers to avoid is a cleaning agent called sodium lauryl sulfate, or SLS, which can be found in everyday household items from Colgate toothpaste to Tide detergent and Honest says can irritate skin. The company lists SLS first in the “Honestly free of” label of verboten ingredients it puts on bottles of its laundry detergent, one of Honest’s first and most popular products.

But two independent lab tests commissioned by The Wall Street Journal determined Honest’s liquid laundry detergent contains SLS.

“Our findings support that there is a significant amount of sodium lauryl sulfate” in Honest’s detergent, said Barbara Pavan, a chemist at one of the labs, Impact Analytical. Another lab, Chemir, a division of EAG Inc., said its test for SLS found about the same concentration as Tide, which is made by P&G. “It was not a trace amount,” said Matthew Hynes, a chemist at Chemir who conducted the test.

Honest disputes the labs’ findings and says its own testing found no SLS in its products.

“We do not make our products with sodium lauryl sulfate,” said Kevin Ewell, the company’s research and development manager.

Honest’s business goes well beyond the detergent, which is the only product the Journal examined. The company, which has raised more than $200 million from private investors, sells more than 100 varieties of products. It has developed a loyal following among its customers, and its line of diapers and other baby-focused products have been particularly popular with young mothers. It sells products online, but also enjoys shelf space at Target Corp. and Costco Wholesale Corp.

Honest said its manufacturing partners and suppliers have provided assurances that its products don’t contain SLS beyond possible trace amounts. Honest provided the Journal with a document it said was from its detergent manufacturer, Earth Friendly Products LLC, that stated there was zero “SLS content” in the product. Earth Friendly in turn said the document came from its own chemical supplier, a company called Trichromatic West Inc., which it relied on to test and certify that there was no SLS.

Trichromatic told the Journal the certificate wasn’t based on any testing and there was a “misunderstanding” with the detergent maker. It said the “SLS content” was listed as zero because it didn’t add any SLS to the material it provided to Earth Friendly and “there would be no reason to test specifically for SLS.” It said the product in question “was fairly and honestly represented” to its customer.

Honest said it didn’t deal directly with Trichromatic and declined to comment further on the certificate. Earth Friendly reiterated that it relied on Trichromatic to test the ingredient.

Honest also disagreed with the methods used by the Journal’s labs, and said the labs tested against a sample of SLS that isn’t the type used in consumer products. Both Chemir and Impact Analytical said they stand by their test results, used the most precise method for quantifying SLS in a consumer laundry detergent and followed standard scientific guidelines.

P&G said it had “no issue” with the level of SLS the tests found in Tide.

Ms. Alba, who is Honest’s chief creative officer in addition to co-founder, declined to be interviewed for this article. Her attorney Bert Fields said, “Jessica Alba and the folks at Honest truly believe that their detergent is free of non-trace SLS and have been assured of that by their suppliers.”

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