The answer to 'why is my toilet foul smell' is that a foul odor coming from your toilet is usually caused by a blockage or buildup in the plumbing system. This can allow sewer gases to escape and create an unpleasant smell in your bathroom.
Some common causes include a clogged toilet, a cracked wax ring, a dried-out P-trap, or a problem with the septic system. Symptoms may include a persistent bad smell, gurgling noises, or slow drainage. To resolve the issue, you may need to plunge the toilet, replace the wax ring, or have a professional inspect and clean the septic tank.