“Log” stands for logarithm, which is the exponent of 10. For example, Log 2 represents 102 or 10 x 10 or 100. Log reduction stands for a 10-fold (or one decimal) or 90% reduction in numbers of live bacteria. Another way to look at it is: 1 Log reduction would reduce the number of bacteria 90%. This means, for example, that 100 bacteria would be reduced to 10, or 10 reduced to 1.
(Source: EPA and FDA)
Log reduction is a mathematical term (as is "log increase") used to show the relative number of live microbes eliminated from a surface by disinfecting or cleaning.
For example, a "5-log reduction" means lowering the number of microorganisms by 100,000-fold, that is, if a surface has 100,000 pathogenic microbes on it, a 5-log reduction would reduce the number of microorganisms to one.
Log Reductions
- 1 log reduction means the number of germs is 10 times smaller
- 2 log reduction means the number of germs is 100 times smaller
- 3 log reduction means the number of germs is 1000 times smaller
- 4 log reduction means the number of germs is 10,000 times smaller
- 5 log reduction means the number of germs is 100,000 times smaller
- 6 log reduction means the number of germs is 1,000,000 times smaller
- 7 log reduction means the number of germs is 10,000,000 times smaller
Download HFI's Log Reduction Reference Chart
