In this case, the sheer number of complaints played a role in the decision. The agency says it is investigating more than 21,000 complaints reported to Chaz Dean Inc. and Guthy-Renker. (Gianna Cesa, a PR representative for Chaz Dean, says the company did not receive this number of complaints.)
Katz says she can't discuss any working hypotheses associated with the investigation, though she did say investigators have no reason to believe the product was contaminated with something foreign, like microbes. For now, the FDA is still gathering information. Officials will look at the product's quality testing and whether there have been any changes to how the product is made.
In an email, a spokesman for Chaz Dean said the company stands behind its products and that "the brand has consistently cooperated with the FDA and will continue to do so."
Dermatologists say hair care products can cause these sorts of symptoms. One common reason is allergy.
"There are thousands of ingredients that are in personal hair products," says Bruce Brod, a clinical professor of dermatology at the University of Pennsylvania. "While most people in the population won't react to them, there's a small subpopulation that will."
Common allergy triggers include surfactants, the ingredients in shampoos and conditioners that make them sudsy, as well as preservatives that increase shelf life and chemicals used to create fragrances.
These allergic reactions can occur regardless of whether a product is "all natural," says Mirmirani. "Lots of plants give people a reaction as well," she says, citing poison oak as an example. And because allergic reactions can take a while to occur, people may not immediately realize a hair product is causing issues.
But there are also causes of scalp problems that have nothing to do with cosmetics, says Nicole Rogers, an assistant clinical professor of dermatology at Tulane Medical School. For example, she says, male-pattern or female-pattern baldness are both common causes of hair loss. Or a patient could suffer from alopecia areata, a disease in which the immune system attacks hair follicles. She says she believes it's unlikely the consumers' complaints are tied to Wen.
Stress, changes in diet and pregnancy can cause hair loss as well, says Anthony Rossi, a dermatologist who serves as a consultant to Chaz Dean's PR firm.
That said, all the doctors told Shots that people with scalp problems should visit a dermatologist and discuss hair products, along with other possible factors. Doctors can do allergy tests on patients to analyze as many as 55 potential allergy triggers. It's important, says Brod, to look at all potential causes of symptoms, rather than looking at Internet chat rooms alone.
"Often, there's a suggestive herd effect," he says. "If somebody says, 'I'm using something and it itches my scalp,' the person next to him will say, 'You know what? Me too.' "
Katz of the FDA also urges people to visit doctors in addition to reporting complaints to the FDA. And if someone decides to switch from Wen to a different conditioner, Mirmirani says, "There's plenty more out there."
Copyright 2016 NPR. To see more, visit http://www.npr.org/.
9(MDAxOTAwOTE4MDEyMTkxMDAzNjczZDljZA004))