A 47-year-old woman showed up at the emergency room near her home in Sacramento, California, suffering from numbness in her hands and face, as well as slurred speech and difficulty walking. 

Her symptoms continued to get worse over the next few weeks, KCRA-TV reports, and she has since slipped into a semi-comatose state. Tests showed that her blood contained high levels of mercury. In order to find out the cause, doctors tested her cosmetic products and traced the source: A pot of Pond's-labeled anti-wrinkle cream, tainted with dangerous levels of methylmercury, which health authorities believe was added by a third party, not by Pond's themselves.

Methylmercury, a substance more toxic than inorganic mercury, can accumulate in the body over time and enter the nervous system. While fish such as tuna contain low levels of it, consuming or coming into contact with too much of it can result in methylmercury poisoning, which can cause poor cognitive function, blindness, and impaired lung function.

It is the same compound responsible for over 1,700 deaths in Minamata city, Japan, after a chemical plant released it in wastewater into Minamata Bay from 1932 to 1968. The compound accumulated in shellfish and other fish in the bay and Shiranui Sea, which then caused mercury poisoning when consumed by the local population. Animals in the area were not unaffected. Before the poisoning was noticed in human populations, residents observed cats making strange "dancing" motions, convulsing and making weird noises before they died, in what became known as "dancing cat fever".

Over the last nine years, there have been over 60 poisonings linked to the less toxic form of mercury, mercurous chloride or calomel, in unlabeled, homemade, or foreign-brand skin creams, usually sold in smaller stores, swap meets, or on the Internet. Some products have been found to contain over 200,000 times the legal limit of mercury, according to the Sacramento County Department of Health Services (SCDHS).

The woman, who is still in a semi-comatose state, is the first case involving the more toxic methylmercury, and the SCDHS is urging the public to stop using similar products and look out for symptoms of poisoning, particularly pregnant and breastfeeding women and children.

“Sacramento County Public Health urges the community to immediately stop using similar skin creams imported from Mexico due to the risk of contamination with methylmercury,” said Sacramento County Public Health Officer Dr Olivia Kasirye, ABC News reports.

“Methylmercury is extremely dangerous to adults and children.”

Symptoms in adults include difficulty concentrating, memory loss, tremors, headaches, and anxiety, while in children you should look out for pink hands and feet, flaking skin, excessive saliva, thirst, and irritability.