For legal reasons, the government’s hands are tied.

That is in part because unlike pharmaceutical companies, cosmetic companies are not required to notify the government of “adverse reaction” reports — even if someone dies.

Image Wen’s Sweet Almond Mint Cleansing Conditioner, which Miriam Lawrence used on the hair of her daughter, Eliana. Credit... Nick Cote for The New York Times

The F.D.A. instead has had to depend on consumers stepping forward, and as of July 7, only 127 reports had been filed to the agency detailing problems with the Wen hair care line. But inspectors sent to the company’s facilities dating back to 2011 learned that complaints to the company and distributor total more than 21,000, the agency said last month.

“You know how the stars were saying it was so good and it made your hair more manageable, more shinier?” said Bonnie Iqbal, 55, of Albany, who last year was among those who sued the company after her hair began falling out. “So I figured, you know, I’d try it.”

Patricia J. Zettler, a health law and policy expert at Georgia State University and a former F.D.A. lawyer, said that under existing law, the agency could take action against the company only if it could prove a product had been mislabeled or contaminated. If the product turns out to be dangerous but legal, the government has no recourse.

“The bottom line is, if the company has not violated the law, there isn’t really anything F.D.A. can do,” Ms. Zettler said.

Even in the absence of federal action, Guthy-Renker, in a “business decision,” agreed in late June to a $26.25 million legal settlement — still not approved by a federal court judge — that would repay up to $25 to every person who has bought a bottle since Wen products were introduced and as much as $20,000 to individuals claiming hair loss or other injury. Yet the product is still being sold, and the F.D.A., other than issuing a notice saying it is looking at the matter, has taken no action.

The Feinstein-Collins bill is intended to eliminate such stalemates. It would, for the first time, require that cosmetics manufacturers report “serious adverse” reactions to their products to the F.D.A. as they come in, as well as create an annual report of all “adverse events.” It would also give the agency the power to order companies to recall products found to be dangerous.