What makes potato salad go bad onions or mayo?

* Onions: Onions contain a high amount of water, which can provide a breeding ground for bacteria. Additionally, onions contain sulfur compounds that can react with oxygen to produce off-flavors and aromas.

* Mayonnaise: Mayonnaise is made with eggs, which are a major source of protein. Proteins are easily broken down by bacteria, which can lead to spoilage. Mayonnaise also contains oil, which can provide a breeding ground for bacteria.

Here are some tips to help keep potato salad fresh:

* Use fresh, high-quality ingredients.

* Wash your hands before handling the ingredients.

* Keep the potato salad refrigerated at all times.

* If you're not going to eat the potato salad within a few days, freeze it.

* Discard any potato salad that has an off odor or flavor.