Yes, you can put your jeans in the washing machine without using detergent, but it might not effectively clean them. Detergents are specifically designed to remove dirt, stains, and oils from clothes, and they play a crucial role in the cleaning process.
If you choose not to use detergent, the jeans might not come out as clean as you'd like, especially if they are heavily soiled. Additionally, odors might not be eliminated without the detergent's cleaning power.
However, if you're in a situation where you have no detergent available, you can still run a wash cycle using just water to remove some surface dirt and freshen up the jeans slightly. It's better than not washing them at all, but for optimal cleaning, it's best to use an appropriate amount of detergent in the washing machine.