(CNN) Complaints of adverse health events related to cosmetic and personal care products more than doubled from 2015 to 2016, according to a study published Monday in the journal JAMA Internal Medicine.

The majority of those complaints stemmed from hair care products.

Northwestern University researchers looked at complaints collected by the Food and Drug Administration from 2004 to 2016. The information came from the FDA's Center for Food Safety and Applied Nutrition's Adverse Event Reporting System, which allows consumers or health care professionals to submit complaints about harm caused by using cosmetic products.

The study found that there were 706 related adverse events reported in 2015 and 1,591 in 2016. Compared with the average number of reports across the 12-year study period, that's a 78% increase in 2015 and a 300% increase in 2016.

However, the lead study author, Dr. Steve Xu , believes the number of adverse health events is probably much higher and more data are needed.

"These numbers are likely underreported. We need better reporting, from both consumers and clinicians," Xu said. "Broadly, the hope of our paper was to continue this discussion to modernize and expand the collection of data about personal care products. If you can't measure it, you can't manage it, was our key point."

The study authors largely attribute increases in reported adverse health events to WEN by Chaz Dean hair care products. In 2014, the FDA announced that it was investigating WEN by Chaz Dean Cleansing Conditioner products because it had received complaints of hair loss, hair breakage, balding, itching and rash. As of November, the FDA had received 1,386 complaints of adverse health events from these products.

In the course of the investigation, the FDA discovered that Chaz Dean Inc. and parent company Guthy Renker LLC had received more than 21,000 complaints. However, under current regulations, the companies are not required to report these complaints to the FDA.

Although the FDA investigation is ongoing, the WEN conditioning products have not been pulled from the market. The FDA has no authority to recall cosmetics products, although it can recommend recalls.

Manufacturers also do not have to receive approval from the FDA before cosmetics go on sale.

In an email, the FDA said that "The law does not require cosmetic companies to share their safety information, including consumer complaints, with the FDA. FDA's data on cosmetic adverse events are limited because reporting is voluntary. The FDA may take regulatory action against cosmetics on the market that do not comply with the laws we enforce, if we have reliable information indicating that a cosmetic is adulterated or misbranded."

Xu said he still thinks most cosmetics are OK to use.

"When it comes to cosmetics on the shelves that are dangerous, it's very hard to prove," Xu said. "In general, cosmetics are a very safe product class."

The Personal Care Products Council said in a statement that it "believes that mandatory adverse event reporting is critically important, which is why we have long advocated for it on Capitol Hill." The council is a national trade association representing the cosmetic and personal care products industry.

"Nevertheless, despite the recent increase in reporting, the fact remains that only a very small percentage of cosmetics products on the market are associated with adverse events. And of those, a fraction are listed as 'serious,' " the council said. "In other words, even with the increase, adverse reactions associated with cosmetics and personal care products are extremely rare."

Dr. Robert Califf , former head of the FDA, said the root of these complaints lies in the FDA's limited ability to regulate cosmetics.

"For cosmetics -- and for dietary supplements -- the FDA's oversight authority remains stuck at the levels established in 1938, nearly 80 years ago," Califf said in an editorial accompanying the study in JAMA Internal Medicine

Sens. Diane Feinstein, D-California, and Susan Collins, R-Maine, introduced a bill in May that would require further regulation of personal care products. If passed, the bill will require the FDA to test certain ingredients. It would also give the agency authority to issue recalls and require more complete product labels and warnings from manufacturers.

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"When you think about harmful chemicals, you can think of two levels," Harley said. "You can think of acute harm and chronic exposure. Acute would be 'I use a cosmetic product, and I get this rash that's almost immediate, or hair loss, or something like that.' It's an extreme reaction that's happening so close in time to when you use the product, it seems it's linked to the use of this product."

Harley, who emphasized that most cosmetics are not harmful, says acute events are most likely the kind reported in the Northwestern study.

"On the other hand, there are chemicals that might, if we use them every day over a long period of time, have small, long-term impacts on our health," said Harley, who conducts research on the effects of chemical hormone disruptors in cosmetics but was not affiliated with the new study.

"These effects may not be obvious on a day-to-day basis, but you know if you've been using this product for 20 years of your life, maybe it would have some sort of health impact over the long-term. And this is why we need more research. With these long-term health impacts, there's so much we don't know."