UPDATE: This post was revised to include comment from the Honest Company.

A new report is calling into question just how honest Jessica Alba's Honest Company has been about how it formulates its growing list of nontoxic products.

According to a Wall Street Journal investigation that commissioned two independent lab tests of Honest's laundry detergent, the product contains sodium lauryl sulfate, or SLS. Honest has put SLS--a common cleaning agent that creates lather and may irritate sensitive skin--on a list of ingredients that its products do not contain.

Honest has become one of the fastest-growing consumer products companies to launch in recent years and has distinguished itself from mainstream brands on the market by promising products that are free of toxic or health-compromising chemicals.

"Our findings support that there is a significant amount of sodium lauryl sulfate" in Honest's detergent, Barbara Pavan, a chemist at the labs Impact Analytical, told the Journal. Honest takes issue with the findings and testing methods, and claims its own tests show no SLS, the Journal notes.

The company's research and development manager, Kevin Ewell, told the newspaper, "We do not make our products with sodium lauryl sulfate."

Honest uses Earth Friendly Products as its detergent manufacturer, which in turn uses Trichromatic West as one of its chemical suppliers. Trichromatic told the Journal that it lists "SLS content" as zero because it does not add any SLS to the material it supplies to Earth Friendly. Earth Friendly, meanwhile, claims that it relies on Trichromatic to test for SLS.

The Journal only tested the detergent, which is one of more than 100 products Honest sells.

The Honest Company issued a statement in response to the report:

"Despite providing The Wall Street Journal with substantial evidence to the contrary, they falsely claimed our laundry detergent contains sodium lauryl sulfate (SLS). To set the record straight, we use sodium coco sulfate (SCS) in our brand's laundry detergent because it is a gentler alternative that is less irritating and safer to use. Rigorous testing and analysis both by our internal research and development teams as well as further testing by external partners have confirmed this fact." 

Honest has faced criticism over its products in the past. During the summer, the company was hit with a rash of complaints over the effectiveness of its "natural" sunscreen. Sunburned customers posted pictures of themselves on Twitter and Facebook. Honest's first response to the kerfuffle was a statement insisting the sunscreen had passed extensive third-party tests and suggesting users may not have applied as directed. Later Alba and co-founder Christopher Gavigan published a more personal blog post promising "we'll do what it takes to make it right," though did not admit any specific wrongdoing.

In September, the company was hit with a class-action lawsuit in California claiming that Honest's products aren't as natural as advertised. And more recently, a second class-action lawsuit was filed in New York in February claiming that Honest "products in fact contain a spectacular array of synthetic and toxic ingredients" and the company's advertising is misleading. Honest has called these suits "baseless."

The three-year-old company was on track to pull in $150 million in revenue in 2014. This year, industry watchers estimate that figure will soar past $250 million, and the company is reportedly considering an IPO. The company's latest funding round of $100 million in August put Honest Company's valuation at $1.7 billion, according to the Journal

The company seems to have no plans of slowing down its torrential pace of releasing new products, which are sold through its website and at more than 4,000 stores, including Target. The brand launched with 17 items, including nontoxic diapers and cleaning products, but now sells everything from toilet paper and infant formula to cribs and a line of makeup.

In April, onstage at Inc.'s GrowCo conference, I asked Alba and CEO Brian Lee if they worried about Honest's fast pace of growth and how they would know if the company started to grow too fast. 

"The way that you know if you're growing too fast is really about the customer and the community," Lee told me. "They'll let you know. Cracks start forming and leaks get bigger. The first thing you see is a decrease in customer satisfaction."