Women are accusing a hugely popular celebrity shampoo brand of making them go bald

Hundreds of women are suing a celebrity-endorsed shampoo brand for allegedly causing bald spots and rashes.

The brand at the center of the lawsuit is Wen Hair Care, which is manufactured and sold by celebrity hair stylist Chaz Dean and Guthy-Renker, the company behind Proativ and other beauty products.

More than 200 customers in 40 states have signed on to the class-action lawsuit, which claims the shampoo - which the company calls "cleansing conditioner" - causes bald spots, severe hair breakage, scalp irritation, and rashes.

Wen is advertised as "gentle enough to use every day" and it's endorsed by celebrities such as Brooke Shields, Alyssa Milano, and Angie Harmon.

Ads for the shampoo claim: "You can never use too much! The more you use, the better the results."

The lawsuit, which was filed by filed by the law firm of Christiansen Davis, claims the product contains harsh chemicals.

"One or more of the products' active ingredients act as a depilatory or caustic agent, either by causing a chemical reaction that damages the hair strand and/or follicle," the lawsuit claims. "The effect of this ingredient(s) render the products dangerous and unsafe for sale as an over-the-counter hair product."

In customer reviews cited in the lawsuit, women described "pulling clumps of hair out of [their] head" and seeing their hair "falling out in gobs daily."

Wen products have largely positive reviews on Amazon, however. Several varieties of the cleansing conditioners have four or more stars on Amazon, with hundreds of reviews.

Some of the negative reviews mention hair loss and hair thinning.

We reached out to Guthy-Renker for comment, and will update this post when we hear back.

In a statement to NBC News, Wen, Guthy-Renker, and Chaz Dean said, "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."

Here are some photos of alleged hair loss included in the lawsuit: