Possible Causes of Bad Smell in Nose
Certain Medications, Beverages, and Foods
Beverages and foods contain microscopic molecules that can stimulate the body’s sense of smell. When we eat or drink, these molecules go through a passageway near the mouth’s roof to reach the sinuses. As the body breaks and digests food, smells are released. Nevertheless, certain products and even medications would cause bad smell in the nose or linger in your mouth. To prevent this, you should limit the consumption of coffee, onions, garlic, spicy foods, nitrites, nitrates, phenothiazines, and amphetamines. 
Sinus infection, also known as sinusitis, is usually caused by bacteria or virus. Regardless of the causes and forms, the condition may fill the nose with an unpleasant smell. In some cases, sinus infection can be caused by a fungus. Compared with viruses or bacteria, fungi are harder for the immune system to defend. This type of sinus infection may be more common in people with a compromised immune system. Identifying the underlying cause plays a key role in treating the condition. In addition to a bad smell in the nose, other common symptoms include fatigue, postnasal drip, facial pressure, and headache.