Your cream or ointment is probably contaminated. But it doesn't have to be

Unless you’re scrupulously careful about keeping your ointments and creams pristine, they are most likely contaminated with pathogenic microbes such as Staphylococcus aureus, a new study reports.

S. aureus, of course, is the nemesis of eczema patients, causing long-lasting, painful skin infections.

There’s about a 30% chance the cream inside an open jar or tube is contaminated with some microbes, although the actual number of organisms is likely relatively small. The chance is twice as high that microbes are teeming on the rim of the container, say Michael Lundov and colleagues at the University of Copenhagen, who conducted the study.

I probably don't need to point out that if your cream or ointment is in a tube, the only way it comes out is past the rim.

The authors used industry standard techniques to culture bacteria, fungi, and yeast from 32 different hand cream products collected from 20 patients. They transferred small samples of the creams to agar plates and counted the number of microbial colonies that grew.

"It is important that the patients exercise care in using creams and limit contact between the opening/edge of the container and their skin," the authors say.

They did not include a control from an unopened jar or tube, which would be interesting because it would indicate how sterile their method was. In the paper they report only that colonies grew in 20 of the 32 tests, but they count the presence of very small numbers of colonies as an indication the hand cream was contaminated. So things may not be as bad as they appear.

What can you do to prevent contamination? In biology, it’s common to take a large quantity of a reagent and parcel it out into small “aliquots.” Then you use one aliquot at a time so you don’t run the risk of contaminating the whole batch. Now, I don’t want to do that with my jumbo jar of Eucerin, but the authors suggest that I might want to use a sterile-ish spoon to take cream out each time I use it—presumably without then putting the spoon back in. I know this method is practical because Nikki, a Twitter user, told me she does this at home.

Good luck keeping your ointments and creams bug-free!