Anyone who has channel-surfed at 3 a.m. and watched celebrity hair stylist Chaz Dean work his magic on the manes of Brooke Shields and Alyssa Milano will be familiar with the WEN hair care range.

Billed as a sulfate-free alternative to shampoo, WEN promises to “take the place of your shampoo, conditioner, deep conditioner, detangler, and leave-in conditioner.”

But the cult favorite products have also attracted controversy. Over the years, horror stories from customers have circulated online—on WEN product forums and sites including Pissed Consumer and Amazon—about WEN’s 5-in-1 Cleansing Conditioners causing hair to come out in handfuls, as well as clogged drains and bald spots.

Now, more than 200 women in 40 states have joined a class action lawsuit against WEN by Chaz Dean and infomercial giant Guthy-Renker in California Federal Court. They claim that the WEN products can cause severe and possibly permanent damage to hair, including significant hair loss to the point of visible bald spots, hair breakage, scalp irritation, and rash.

According to court papers, nurse practitioner Amy Friedman bought the WEN Sweet Almond Mint basic kit in January of 2014 for $29.95, and within two weeks “began losing substantial and abnormal amounts of hair.” The shedding continued, she said, for approximately three weeks after she stopped using WEN, and eventually resulted in her losing “one quarter to one third” of the hair on her head. In an attempt to regrow her hair, she claims that she was forced to spend a substantial amount money on vitamins and extensions to mask the loss.

The suit alleges that Friedman’s complaint is only the tip of the iceberg—and states that the number of potential plaintiffs in the class suit could number “in the thousands or tens of thousands.”

Indeed, a Google search brings up hundreds of negative reviews. “I was a professional model with beautiful long natural hair. After using this product my scalp and face broke out in boils and my hair fell out in chunks,” one woman wrote. “This shampoo destroyed my life.”

Another user said that she loved the product at first—but after five months “I noticed a bald spot the size of a half dollar at the crown of my head.”

Yet just as many five-star WEN fans claim that the products have been the best thing that has ever happened to their hair—and five-star reviews have led to the products repeatedly ranking #1 under hair care on Amazon.

WEN has been a huge cash cow for Guthy-Renker, reportedly raking $100 million in only its second year, and has made Chaz Dean as famous as many of his celebrity clients. The suit has been shocking for many customers due to the holistic lifestyle and organic philosophy that Dean espouses in his salon, infomercials, and on Instagram.

According to the bio on his website, Dean started out as a hairdresser in Los Angeles and created the formula that became WEN by mixing the ingredients in his sink. His celebrity-to-the-stars status was cemented after he used Sweet Almond Mint cleansing conditioner on Alanis Morrissette for her Grammy appearance in 1999.

Dean has remained down-to-earth and likable in spite of his fame, and is a regular on reality shows including Flipping Out and Celebrity Apprentice, has purchased properties including a Greenwich Village townhouse for $10 million, and flies his four rescue Labradors on a private jet in between their WEN grooming sessions and twice-daily hikes.

According to court papers, the company’s website makes statements such as “WEN® is gentle enough to use every day,” and “WEN® isn’t like an ordinary shampoo so you want to use more of it, not less,” and “You can never use too much! The more you use, the better the results.”

Not only did the company fail to warn customers of the dangers, the suit alleges, but Guthy-Renker also apparently removed negative online reviews about the products, and blocked or erased comments about hair loss from the WEN Facebook page.

Despite this, many are still available: “Not only did it not clean my hair, it made it look like I combed it out with a pork chop,” one woman wrote on the WEN product forum. Another said that she was distressed at having to explain that her hair loss was “not from chemo.”

Exactly which ingredients may be causing hair loss remains a mystery. The complaint alleges that “the WEN products at issue contain a caustic ingredient that causes a chemical reaction and damages hair and follicles,” as well as “numerous harsh chemicals and known human allergens.”

But the first four ingredients on many of the cleansing conditioners are listed as “water, glycerin, cetyl alcohol, and cetearyl alcohol.” Alcohol can be drying, but it is widely used in hair care products. Another ingredient, hydroxycitronella, is banned in the EU because it is known to be a human immune system toxin.

In the complaint, Guthy-Renker categorically denies that its products are in any way defective or responsible for hair loss. But over the years, many stylists have swapped their own theories over the shampoo bowl. “WEN seems to be good for certain hair types, especially those that are coarse or frizzy,” says Kelsey Smart, a stylist at Fox & Jane salon in New York. “But for women with fine hair, it becomes more important for the scalp to stay really clean—otherwise, product can build up and lead to breakage.” Ironically, women who need a squeaky-clean scalp may be in most need of the sulfates that Dean has tried so diligently to avoid.

Dallas-based attorney Amy Davis, lead counsel for the victims, says that the firm has hired chemists to perform tests. “What we understand about the product and how it causes hair loss is it contains virtually no cleanser,” Davis told CBS 11 in Dallas. “It’s like using lotion to wash your hair, so instead of removing the product, when you rinse it off, it just becomes impacted in your hair follicle.”

And the plaintiffs could have a tough road ahead, since experts say that determining the cause of hair loss in women can be extremely complicated. According to the American Dermatological Society, it can be caused by a number of factors from genetics, hair dryer and flat iron use, to hormonal changes from pregnancy. Dermatologists often have to turn detective and perform a series of tests in order to determine the cause.

Narrowing down the offending ingredient(s) becomes even more complicated due to the fact that WEN is sold all over the world, so there are multiple formulas available—as well as various knock-offs. “Official” WEN products are sold through www.chazdean.com, Guthy-Renker, Sephora, and QVC.

Tara Bell, who describes herself as a 52-year-old former hairdresser, wrote on the WEN message board that she loved the Lavender Cleansing Conditioner that she bought from QVC but had an extreme reaction to a bottle that was ordered from Amazon. (Amazon is meant for international buyers, but many U.S. customers buy from the site in order to avoid the monthly billing of buying direct from WEN.)

“After I rinsed it I noticed some of the bleached hair in the front was ‘sticky’ like glue and actually breaking off. I am in shock,” she wrote. “I have now been super paranoid about the hair I find in the drain and have been researching and seeing all the horror stories about lawsuits. There are different formulas depending on who you buy it from,” she added.

Jillian, a WEN customer service representative who posted on the company’s website, confirms that Guthy-Renker’s version of WEN is slightly different than the one sold via www.chazdean.com and QVC.

“Because of regulations on products sold internationally, the ingredients through Guthy-Renker have had to be changed slightly. Chaz worked very hard to make sure that the quality and philosophy behind WEN is still upheld, and that product performance would be identical,” she wrote.

For now, the parties are heading to mediation—so the reasons for hair loss may remain a mystery.

“The parties are attempting to settle their differences outside of court and we have agreed to refrain from any extrajudicial statements about the case in the meantime,” Davis told The Daily Beast.

Guthy-Renker did not immediately reply to a request for comment, but said in a statement: “Importantly, there is no scientific evidence to support any claim that our hair care products caused anyone to lose their hair. There are many reasons why individuals may lose their hair, all unrelated to WEN hair products. We intend to vigorously contest the allegations made against our products. And, we encourage any customer with any questions to contact us.”