Flat poops can happen due to changes in your diet. Some health conditions, including constipation, can cause long or flat poop. If unexplained changes last a few days, consider talking with a doctor.
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What causes stringy poop?

Stringy poop can be caused by a lack of fiber and fluids in your diet. Some infections can cause stringy poop, but your poop ...
Hemorrhoids can cause or contribute to constipation. In some cases, they may even worsen it. However, the reverse is also true, with constipation being an underlying factor for developing hemorrhoids.