Your smartphone case might be bugged.

Studies have found that molds and mites easily proliferate on the covers of smartphones, which generate heat and provide favorable environments for the minute lifeforms.

“I think there is no actual harm to the health (of smartphone users),” said Nobuo Hamada, a researcher at the Osaka Museum of Natural History, who has studied molds inhabiting the living sphere of humans. “But it is necessary to pay a little consideration to cleanliness. If you regularly wipe the inside of the covers, you can drastically decrease the presence of molds (and mites).”

Hamada checked the covers of 116 smartphones used by people who cooperated with his research.

In his first full-scale study conducted in March and April 2014, he swabbed all parts of the inside of the covers using a physiological salt solution, and then separated the stains from the cotton swabs.

He planted the stains in an agar culture medium and counted the numbers of molds.

Molds were detected from the covers of 48 smartphones, or about 40 percent of the total.

Thirty-two of the covers had fewer than 100 molds, while 10 had mold numbers ranging from 100 to 1,000. Two had 1,000 to 10,000 molds each.

Four smartphone cases exceeded the 10,000 level, and the moldiest one contained 560,000.

Inside some of the covers, lumps of molds spreading like spider webs were visible to the naked eye.

In another study conducted by Hamada in June 2015, common grain mites, which are about 0.3 millimeter long and feed on mold, were detected on the inside of smartphone covers.

Many of the detected molds were Aspergillus and blue molds that favor humid conditions.

Dust and moisture can easily accumulate inside smartphone covers. In addition, the cases are warm, even in winter, because the smartphones generate heat.

Molds and mites can proliferate under such conditions.

Hamada also looked into the relationship between the proliferation and the length of use of the covers.

He found that molds started appearing in the cases after about a month of usage.

Cases used for periods ranging from one to two years contained an average of 26.4 molds, his study showed. For cases in use for more than two years, the average number of detected molds soared to 73.1.

The cases of female smartphone users contained an average of 24.0 molds, while the figure was 28.8 among male users.

Teenage smartphone users had an average of 20.2 molds in their cases, while the corresponding figure was 47.3 for those in their 30s or older.

The cases of smartphones usually kept inside bags had an average of 20.7 molds. The average figures were 23.8 molds for smartphones kept in breast pockets and 32.5 for those stored in trouser pockets.