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Andy Nguyen
By Andy Nguyen October 19, 2022

The dark spots on a potato aren’t from 'throat mold' and are safe to eat

If Your Time is short

  • Ring rot is a bacterial infection that breaks down a potato’s vascular system. It is not harmful to humans and potatoes with ring rot are safe to eat.
  • Harmless dark spots can form on a potato chip because the potato it was made from was bruised or converted its starches into sugars. Discoloration of the potato’s vascular system can also cause the spots.

Potato chips are one of the most consumed snacks in the United States, with an estimated 1.85 billion pounds eaten each year, but a recent Facebook post claims people should look twice before taking a bite. 

The post features photos of ridged potato chips with dark spots on the surface along with a photo of a raw potato’s cross-section with a dark ring around its interior.

"The chips that look like this, we eat it and say it is burnt," the Oct. 7 post said. "It’s not burnt. It’s infected with throat mold, which means it’s forbidden to be eaten forever, and it must be thrown away. Please be aware of your children." 

"Throat mold" isn’t a real condition affecting potatoes and an expert we talked to said the ring shown in the raw potato was likely caused by a bacterial infection that affects potatoes, but not the humans who eat them. The rings on the potato chips are also harmless. 

The video was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Meta, which owns Facebook and Instagram.).

Most plants contain a vascular system with tissue called the xylem and phloem, which distributes water, minerals and food across the plant. In potatoes, this system encircles the interior of each spud and is known as the "vascular ring." 

Robert Wilson, a farm adviser and director of the Intermountain Research Extension Center at the University of California’s Division of Agriculture and Natural Resources, said he knows of no plant infection called "throat mold." 

A Google search could not find any references to potatoes and "throat mold" outside of unsubstantiated social media posts similar to the one on Facebook.

Wilson said the raw potato’s vascular ring in the Facebook post is likely infected with ring rot. Ring rot happens when a bacteria infects a potato plant, causing its leaves to wilt and the vascular ring in a spud to break down into mush. 

Potatoes with ring rot are safe to eat, but Wilson said most commercial processing and packing sheds would reject infected potatoes before they are sold to the public for aesthetic reasons. 

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"Most plant diseases do not carry over to humans, and I’m not aware of anyone becoming sick from eating potatoes with ring rot or dry rot," he said. 

The photo in the Facebook post is the same one the British Agriculture and Horticulture Development Board uses as an example of a ring rot infection

Wilson said the dark spots on the chips are unrelated to ring rot and are common for potatoes used for chips. Discoloration in potato chips is cosmetic and they are still safe to eat. 

"(They) are dark spots or dark coloring from bruising, changes in sugars during storage or vascular discoloration," he said. 

Bruising can happen because of the way a potato has been handled or stored. Potatoes can also convert their starches into sugars, which results in more browning during frying. 

Vascular discoloration can happen for several different reasons, including stress a potato may experience while it grows or when the vine of a potato plant rapidly dies.

Our ruling

A Facebook post claims to show an image of a raw potato and potato chips infected with "throat mold" that should be thrown away and not eaten. 

We found no references to an infection called "throat mold," and an expert told us the raw potato likely had ring rot, which is an infection of a potato’s vascular system and doesn’t harm humans. 

The dark spots on a potato chip are also harmless and safe to eat. 

We rate this claim Pants on Fire!

Our Sources

Facebook post (archive), Oct. 7, 2022

Smithsonian Mag, "How the Potato Chip Took Over America," January 2022

Britannica, "See how the xylem carries food up from the roots and how the phloem transports food down from the leaves," Oct. 14, 2022

Email with Robert Wilson, Oct. 16, 2022

Agriculture and Horticulture Development Board, Ring rot, accessed Oct. 14, 2022

Eat or Toss, "Brown spots on potato chips," Dec. 8, 2020

University of Nebraska-Lincoln, Vascular Discoloration, accessed Oct. 18, 2022

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The dark spots on a potato aren’t from 'throat mold' and are safe to eat

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