It’s true that one recently found substance in human body odor, called 2-Nonenal, tends to increase with aging, according to a study from researchers in Japan published in the Journal of Investigative Dermatology.

The body odor of people between the ages of 26 and 75 was analyzed. The researchers found that 2-Nonenal, which has an unpleasant greasy and grassy odor, was detected only in the participants ages 40 or older.

So, what causes body odor (aka B.O.)? Most often, it’s the bacterial breakdown of sweat that causes an odor. Perspiration, itself, is practically odorless.