WASHINGTON (Reuters) - Chattem Inc. failed to notify U.S. health officials about new cautions added to its Icy Hot heat therapy patches after getting more than 168 complaints, according to a letter released Tuesday.

In a warning letter to the company, the U.S. Food and Drug Administration also said Chattem did not disclose the reported problems within the time period required by law.

Chattem also did not tell the FDA it was changing the wording on the product's label to help consumers avoid burns and other skin irritations after it received the complaints, the agency said in the letter dated June 6.

The FDA issued the warning after inspecting the company's Chattanooga, Tennessee, plant in February. In the letter, FDA officials acknowledged the company's earlier response to some problems but said it was inadequate.

It was not immediately clear how many consumers were seriously injured or otherwise harmed by the patch, and representatives for Chattem did not immediately return a call seeking comment.

Icy Hot aims to help prevent muscle pain through the use of menthol, a mint extract that produces a cooling sensation. The patches come in different shapes to adhere to the back and other sore body parts.

The FDA said the product's label did not properly explain its warnings or caution that certain users such as children should not use the patches.

"The duration of use of 'up to 8 hours' raises significant clinical concerns as this duration exceeds the established time at which a 2nd degree burn has been shown to occur on human skin at the target temperature of the patch," the letter also said.

"The labeling needs to provide adequate directions for use with respect to the duration the device is to be applied to the patient's skin," it added.

FDA officials issue dozens of warning letters a year and can impose fines, product seizures and other penalties, although most are resolved without such measures. The agency said Chattem has 15 days to notify the agency about steps it was taking to correct the problems.

The letter was posted to the FDA website Tuesday at http://www.fda.gov/foi/warning_letters/s6810c.htm