If you've noticed mucus gathering in the back of your throat, or have recently had a sinus infection or bout of allergies, there's a good chance post-nasal drip may be what's contributing to your bad breath.

"Post-nasal drip presents when excessive mucus is produced by the nasal mucosa [and it] accumulates in the back of the nose and throat," Dr. Monica Tadros, an Ear, Nose, and Throat doctor based in New Jersey and NYC, tells Bustle. She says the "post" in post-nasal drip refers to "back" of the throat. And that's where the smell is coming from — far outside the reach of your toothbrush.

A severe cold, and the resulting post-nasal drip may lead to bad breath. But full on throat infections can, too. As Tadros says, "Throat Infections, such as strep throat may also be a cause of bad breath."

Symptoms of strep throat include pain when swallowing, swollen lymph nodes in your neck, fever, chills, and headache. If you have strep throat, it may be to blame.

Tonsil stones are another common culprit. "These are calcified deposits that can harbor bacteria and food particles that are decaying," Alvin H. Danenberg, DDS, a Periodontist and Certified Functional Medicine Practitioner, tells Bustle.

Tonsil stones hang out in the folds of your tonsils, and if you don't remove them, they can start to fester and create a bad smell in your mouth. An ENT doctor may be able to help you out, but there are multitudes of videos online suggesting ways to remove them yourself at home, with the likes of Q-Tips and water picks.

If you have bad breath that doesn't resolve with brushing and flossing, it could be due to an internal health issue. As Townsend says, these issues include acid reflux, GERD (Gastroesophageal reflux disease), and other stomach problems, all of which can cause smells to creep up from your insides. Speaking with your doctor on how to treat your acid reflux can help to improve the problem.

If you don't drink much water, or have a naturally dry mouth, a lack of saliva may be to blame. "Since there is minimal saliva or no saliva flowing, bacteria will not get 'washed away,'" says Danenberg. "As the bacteria grow and food particles accumulate, these bacteria will create odors from the breakdown of the foods — especially sulfur-containing foods. Without the saliva to flow abundantly, the odor concentrates and infections can begin to take hold." If this seems to be an issue for you, try drinking more water throughout the day or consulting with your doctor about how to help these symptoms.

Speaking of dry mouth, another thing experts say may make bad breath worse is alcohol, including the kind found in most mouthwashes. "What most people don't realize is that alcoholic-based mouthwashes just temporarily mask bad breath and can actually make it worse," Suhail Mohiuddin, DDS, co-founder of SmileCycle, tells Bustle. "Alcohol naturally dries out your mouth, which in turn leads to more odor." And that's why you should be on the lookout for mouthwashes that don't include alcohol, so you can get that minty fresh feeling, without drying out your mouth.

Ever heard of biofilm? It's a totally normal plaque that coats your teeth and tongue, and leads to bad breath. "There are some nasty bacteria that can take up residence on your gums and tongue and they can produce stinky sulfur compounds," Sandra J. Eleczko, DDS tells Bustle. To get rid of it, definitely keep brushing. But also throw in some other flourishes, too. "Flossing [and using] water picks or other devices to clean between your teeth where your toothbrush doesn't go is essential," she says.

Experts say that for smokers, brushing might not make much of a difference when it comes to improving breath. "As if you needed another reason to quit, cigs are just as bad for your breath as they are for your heart," Sophia Borghese, consultant for Southern Dental Care DDS tells Bustle. "Smoking causes a mouth odor on its own, and in return, leads to gum disease which also causes bad breath."

Bad breath may also come from your nose and sinuses, in the form of sinusitis. "When the sinuses become blocked, bacteria collects within them causing bad breath," Dr. Kalpana DePasquale, board-certified Otolaryngologist and founder of KalVera Skincare, tells Bustle. Using a neti pot can help flush out your sinuses. But a trip to the doctor may be a good idea as well.

"If you recently [ate a] garlicky or oniony meal, it’s going to catch up to you later," says Borghese. "These are foods your bloodstream loves, so as soon as they’re in your system, the chemicals end up in your lungs and breath."

There is hope, though. Borghese says eating celery and apples can help neutralize the odor in your mouth and bloodstream, and thus freshen your breath.

Even if you are brushing, food particles may be left behind on and between your teeth, and lead to tooth decay. As Dr. Bobbi Stanley, DDS tells Bustle, "Tooth decay, gingivitis, periodontitis, or any mouth sores related to other conditions can cause bad breath."

But there is something you can do about it. "My first tip is to check with your dentist on your regular dental hygiene routine," Stanley says. "They'll be able to spot any places in your mouth where you're not brushing or flossing well enough. They may be able to recommend better techniques or some tools (like a tongue scraper) that can help you clean your teeth more effectively between visits."

By taking good care of your oral health, and seeking treatment for other health issues that can create smells in your sinuses, throat, and stomach, then experts say your breath will be fresher between brushing.