You've probably seen an infomercial for WEN hair-care products starring celeb hair stylist Chaz Dean. Some customers claim the line cleansing conditioners led to hair loss.

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If you’ve ever spent a sleepless night channel-surfing your TV, you’ve probably seen an infomercial for WEN hair-care products, which star celebrity hair stylist Chaz Dean and A-list clients, like Brooke Shields or Alyssa Milano. The brand's sulfate-free cleansing conditioner was a leader of the no-shampoo movement, helping to make non-lathering cleansers the stars of the market. But now the line is famous for another reason: a class-action lawsuit filed in a California federal court against Chaz Dean and Guthy-Renker, the direct-marketing company that sells WEN.

A group of 200 women in 40 states claim that the products 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.” Some of the women in the case are representing their children because they are minors.

Angry customers have rushed to social media to share their own stories:

The class-action lawsuit also alleges that Guthy-Renker—which also owns the skin line Proactiv—deleted negative comments from the WEN Facebook page, though there are still negative posts claiming hair loss and other issues there now.

However, others have weighed in with positive reviews on Facebook and on sites like Amazon and Sephora as well.

The case is particularly tricky because no one has been able to get to the—no pun intended—root of the problem. The suit claims that WEN products “contain one or more active ingredients that act as a depilatory or caustic agent, causing a chemical reaction that damages the hair strand and/or follicle.”

But Mary Gail Mercurio, MD, Professor of Dermatology, University of Rochester School of Medicine and Dentistry, tells Health that there isn’t an ingredient listed on the bottle that works as a depilatory. “Bottom line, there are myriad of reasons women lose their hair,” she says. “These few pictures all suggest different types of hair loss. If the product contained a depilatory or caustic ingredient as suggested, the hair loss would not impact just a subset of women who used the product. Any hair loss process that causes scarring of the hair follicle would first have to damage the overlying skin to an obvious and significant extent.”

WEN continues to stand by its products, publishing a statement on Facebook reading in part, “We have great sympathy for anyone experiencing hair loss or scalp issues, but there is no scientific evidence that points to the WEN brand as the cause."

Joe Hixson, a Guthy-Renker spokesman told People, “With well over 10 million WEN products shipped since 2008, our customers’ overwhelmingly positive response to WEN is a testament to the benefits it can deliver for its users. These benefits are reflected in consistently high rankings from independent consumer product sites as well.”

Update (Dec. 22, 2015): "There are many reasons why individuals may lose their hair, all unrelated to WEN hair care products," Hixson adds in an e-mail to Health. "WEN labels comply with all regulations. Further, the suggestion that any ingredient in WEN is banned in any geography is patently false," responding to rumors that have appeared in social media posts.

“Hair loss in women is a very common condition stemming from a variety of different causes as I see in my practice on a daily basis,” says Dr. Mercurio, including anything from genetics to hormonal changes from pregnancy to overusing hot styling tools like hair dryers and curling irons. “It is very possible that the women using this product do have a hair loss condition that is completely unrelated. Only by examining the affected women's scalps can the precise cause of the hair loss be determined.”

The WEN products say that they don't contain "harsh sulfates found in some ordinary shampoos." Instead they tout natural ingredients like chamomile extract and wild cherry bark.

But just because products are natural doesn’t mean they can't hurt you or cause a reaction. “Natural ingredients can, in fact, be as harmful as synthetic ingredients,” says Dr. Mercurio. And thanks to lax regulations in the beauty industry, it’s often up to brands to conduct their own testing.

Dr. Mercurio recommends doing a patch test before trying any new product (apply the product to the thin skin on the inner area of your arm to see if you react), especially if you have sensitive skin. “So many patients are focused on having non-synthetic or natural substances for all purposes skin- and hair-related, but I routinely say several times a day that poison ivy is natural and can have dire consequences to the skin. A skin or hair product that is natural doesn’t make it any safer.”