Sewer gas contains hydrogen sulfide, methane, ammonia, and carbon dioxide. Prolonged low or high levels of exposure to sewer gas can cause headaches, fatigue, nausea, dizziness, poor concentration, sinus infections, pneumonia and more. Fortunately, you will usually smell a sewer odor when gasses are seeping into your home. This is why it’s so important to call a licensed plumber as soon as you notice the above signs of a sewer problem.