SAN DIEGO -- Kathryn Henley of San Diego said she used a popular over-the-counter-cold product that stole her sense of smell.

"I started using Zicam a couple of years ago. It was recommended by some people I work with," Henley said.

Her colds were less severe, but when she was healthy, she realized things didn't smell the same.

"Everything smelled so bad," Henley said.

After a while, Henley said she couldn't smell much at all.

Henley went to the University of California San Diego's nasal dysfunction clinic for help. Doctors said she is one of five patients in the last year who have lost their ability to smell after using Zicam.

"They took a bottle of Zicam held it to their nose to sniff it. They took a deep sniff and that's important mistake," Dr. Terence Davidson said.

"It was my natural inclination. I think most people's natural inclination is to sniff it," Henley said.

The problem is the main ingredient in Zicam called zinc gluconate. It is a poison to the cell receptors in the upper nose, according to Davidson.

"They are just bare nerve cells and so zinc applied topically to them is guaranteed poison," Davidson said.

No where on the product is a warning about the serious side effect. The only caution on the box or insert is "to avoid irritation, do not sniff up gel."

Davidson said it is unlikely Henley's ability to smell will return.

"The majority of patients have no return of function, so it's a permanent smell loss," Davidson said.

The Food and Drug Administration is investigating complaints from consumers around the country.

"If I were the FDA, I would take the product off the market," Davidson said.

Davidson said there have also been complaints about another product called Cold-eeze, which also contains zinc.

Manufacturers of both cold remedies said their products are safe and no studies have shown the zinc products caused anyone to lose their sense of smell.