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An Oakland watchdog group has sued four companies and plans to sue dozens more for allegedly manufacturing or selling shampoos, soaps and other care products without attaching labels warning consumers that they contained high levels of a carcinogen.

The suit, filed Tuesday in Alameda County Superior Court by the Center for Environmental Health, accused Walgreens, Lake Consumer Products, Vogue International and Ultimark Products of selling products that allegedly had cocamide diethanolamine, or cocamide DEA.

The group said it intends to sue more than 100 other companies that make or sell such products. The organization listed Walmart, Trader Joe’s, Kohl’s, Target, Rite Aid, Sears, T.J. Maxx, Sephora and Colgate Palmolive.

Cocamide DEA, which is used to make foam and bubbles, was named last year as a carcinogen under Proposition 65, which requires warnings for consumer products with harmful amounts of certain toxic compounds. The chemical was added after the International Agency for Research on Cancer declared it a possible carcinogen in humans.

“I don’t think anybody wants to add one more thing to the list of cancer-causing chemicals that we’re exposed to,” said Caroline Cox, the Center for Environmental Health’s research director. “There’s lots of ways to make shampoo without it. This is one we don’t really need.”

The state gave companies one year to comply after adding cocamide DEA to its Prop. 65 list in June 2012. This summer, the Center for Environmental Health bought shampoos and other products from Bay Area stores and online retailers and had them independently tested. The analysis showed that 98 products contained cocamide DEA.

While the state has listed cocamide DEA, it has not yet declared a specific limit for the chemical in products, but Cox said tests show the identified products have cocamide DEA at levels “way above” the state’s general standard for carcinogens.