After two weeks of wear, a pair of jeans will have grown a 1,000-strong colony of bacteria on the front, 1,500–2,500 on the back, and 10,000 on the crotch.

After two weeks of wear, a pair of jeans will have grown a 1,000-strong colony of bacteria on the front, 1,500–2,500 on the back, and 10,000 on the crotch.

What Kinds of Germs Are on Jeans?
Your jeans get exposed to all sorts of stuff in the course of an average day, like:
1. Pollen.
2. Dust and dust mites.
3. Dirt.
4. Mold spores.
5. Food particles.
6. Dead skin cells.
7. Oil.
8. Sweat.

Can You Sanitize Your Jeans by Putting Them in Your Freezer?
To kill bacteria, you typically have to reach 80 degrees below freezing. Since freezers sit around zero to four degrees, they’re nowhere near cold enough.

How Often Should You Wash Jeans?
A good rule of thumb is to wash them every two to three wears, as often as you would wash your bras. And throwing your jeans in the wash when:
1. They are visibly soiled or stained.
2. You’ve been sweating to the point where moisture has wicked into the jeans.

Source