Shelby County Health Department/Facebook
The Shelby County Health Department (SCHD) has stopped the distribution of the state’s face masks over concerns about a chemical with which the masks have been treated.
The department announced the move in a news release Monday morning. The masks had been given away at all health department locations since May 7th.
The black, knitted face masks are treated with Silvadur. According to the department, it is an anti-microbial agent applied to fabrics to reduce the growth of odor-causing bacteria. Only trace amounts of the chemical are applied to the fabric and the chemical diminishes each time the mask is washed, according to the manufacturer. 
CDC
“Until more information is made available about Silvadur and its application to the masks, SCHD has stopped all distribution of the masks and is asking partnering agencies to also stop distributing them,” the department said in a statement Monday morning. “Anyone who has one of the masks and has safety concerns about it should stop wearing it and wear an alternative facial covering.”
The department continues to recommend wearing a face mask where social distancing is difficult to maintain. The Centers for Disease Control and Prevention has information and guidance about facial coverings, including instructions for making a cloth facial covering, on its website here.