Eating moldy food can cause allergic reactions and diseases. By the time mold is visible on the surface of food, thin threads of mold have typically grown deep into the food. If you see any mold on food, it's usually best to throw it away.
Molds are fungi that release spores into the air to reproduce. The main body of the mold is not easily seen and consists of threadlike growths throughout the food, while the colored mold that you see on the surface of food is only the spores. By the time the mold is visibly producing spores, the food is filled with tiny threads of mold.
For the many people who have mold allergies, eating mold may cause respiratory problems, coughing, sneezing, eye or skin irritation, headaches, or nausea. Some molds produce toxins that can cause diseases, such as aflatoxin, which can cause cancer.
Inspect food carefully for mold before you buy it. To discourage mold growth, keep perishable foods refrigerated, and keep your refrigerator, dishcloths, and sponges clean.
Should I Eat This?
When you notice a small spot of mold on food, you may be tempted to cut off the moldy part and eat the rest. According to the USDA, this is not safe for soft foods such as fruit and baked goods, because the mold is actually growing throughout the food. However, it's okay for foods such as hard cheeses and sausages, because mold growth cannot penetrate very far into harder foods.
Some food molds are beneficial. Penicillin (an antibiotic) comes from a bread mold, and some types of cheese are manufactured using molds that are safe to eat.