A lasagna that you cooked six days ago sits in your fridge . Can you eat it?

According to The Ultimate Mold Guide, a casserole like lasagna keeps fresh inside the refrigerator for between three to five days after cooking. The reason it doesn’t last longer? Mold!

The white and green fuzzy stuff that grosses us out when we spot it in the fridge actually plays an important role in the environment. Without mold, no plant or animal would break down.

Sometimes mold is safe to eat, like the kind on some of our favorite cheeses (We’re looking at you brie, camembert, and Roquefort). Other times mold is a health hazard, including when you spot it on soft fruits and vegetables, leftovers, deli meat, hot dogs and condiments. Harmful mycotoxins can form in your body after ingesting or inhaling mold, so never eat or sniff food you think went bad.

Usually the mold you see is one of the four common molds, Alternaria, Aspergillus, Cladosporium, and Penicillium, according to The Mold Guide. But what the eye spots can also just be the very beginning – it’s possible the mold has penetrated deep inside the food. (One exception is hard fruit such as an orange. With such a thick outer rind, it could be that the flesh is perfectly fine to eat.)

Below is a helpful chart to determine how long it takes for your favorite pantry staples to good bad. All the food represented in the guide is fresh, raw or whole.