A class action complaint against the actress and her partners has been filed by Missouri housewife Margo Smith. She claims Honest bosses "deceptively marketed" the firm's "popular consumer liquid laundry detergent, dish soap, multisurface cleaner and other products" as not containing sodium lauryl sulfate.

Tests have found "significant amounts" of the cleaning chemical.

A similar lawsuit concerning the company's alleged mislabelling of products was filed in New York in February (16), while Honest was also hit with two class action lawsuits last year (15) over its sunscreen.

The Honest Company partners responded to the latest sodium lauryl sulfate test results, reported in the Wall Street Journal, by insisting the brand uses sodium coco sulfate.

The company's bosses accused reporters of not testing for SCS, which they insist is "less irritating and safer to use".

"We also want to dispel the myth that Sodium Lauryl Sulfate (SLS) and Sodium Coco Sulfate (SCS) are the same. They are not," a statement read.

The Honest Company was founded by Alba in 2011 and valued at $1 billion last year (15).