If sweet potatoes appear to rot, it may be caused by soft rot or black spot disease, the initial germs infected the surface of sweet potatoes, black round spots, 2 to 3 days after the spread to the whole piece of sweet potatoes, will begin to rot and emit a foul odor. This condition is not edible.

But not in the sweet potato surface of the black spots are disease, in addition to soft rot and black spot disease will cause sweet potato skin black spots, there are two possible reasons will also cause the sweet potato skin black spots, if the sweet potato in the harvest, may be due to collision with each other caused by the flow of milk, and milk contains a large number of antioxidants polyphenols and oxygen in the air, and produce black spots, but the black spots are not harmful to human health, but they are not harmful to human health, they are not good for human health. This kind of black spots have no adverse effect on human health.

Another possible cause of black spots is the post-harvest healing process. Processors usually place sweet potatoes in a facility with a temperature of 30°C and a humidity of about 95% for 4 to 10 days, so that the wounds in the skin of the sweet potatoes can form a black corky layer, preventing the invasion of pathogenic bacteria, and increasing the time of storage, which does not have an effect on the human body.