Massachusetts Public Health Commissioner Monica Bharel took the stand in state court Friday to defend the state's emergency ban on vaping products, saying it is still uncertain what products are making people sick.

Vaping companies have challenged the ban in Suffolk Superior Court, saying the overwhelming majority of lung illnesses have been caused by an oil connected to THC-based products — the active ingredient in marijuana — and not nicotine-based products. Judge Douglas Wilkins said he will rule Monday morning on their request for an injunction to lift the ban.

The companies argue that the ban should be lifted because it makes no distinction between THC-based and nicotine-based products, and wasn't based on a scientific analysis of the risks.

But Bharel rejected the idea that nicotine-based vaping products are not the culprit in the nationwide epidemic of respiratory injuries. "We do not know the cause of this e-cigarette and pulmonary related illness," she said. "The CDC does not know the cause, the FDA does not know the cause. In many of the published peer reviewed articles it is clearly stated: We do not know the cause of this illness."

On Sept. 11, Bharel ordered medical professionals to report cases of vaping-related illness. Since then, the state has reported to the federal Centers for Disease Control 10 confirmed cases and 19 suspected cases of vaping related lung injury.

One woman in Massachusetts has died from the injuries, and Bharel said in that case, the victim had been using nicotine-based vaping products. She tested negative for THC.

But Michael Siegel of Boston University's School of Public Health testified that reports from around the country are increasingly concluding that black-market THC cartridges are the culprit. He noted that Utah health officials concluded earlier this month that nearly every case they had seen involved unregulated THC cartridges.

"From a public health perspective, I do not see any rational basis for banning nicotine containing e-liquids that are sold in retail stores," Siegel said.

Companies that make and sell vape products have asked the court to overturn the four-month ban on vape sales that Gov. Charlie Baker and the state's Public Health Council issued on Sept. 24. Their legal argument revolves around whether the state had the authority to issue the ban without the traditional requirements of a rulemaking process, such as detailed scientific findings and opportunity for public comment.