What’s the best way to treat the common cold?

Throughout history, one persistent ailment has inspired a variety of treatments. In ancient Egypt, doctors used incantations and breast milk remedies. In 18th century Europe, bloodletting was a popular choice.

And when President Calvin Coolidge was afflicted in 1924, his ill-advised solution was inhaling poisonous chlorine gas. These are just a few of history’s many creative attempts to soothe the common cold. Today, pharmacies are filled with a seemingly mountainous assortment of cold remedies.

But how do these products work? And are they effective? While colds are caused by a variety of viruses, their nasty symptoms aren't actually produced by the viruses themselves.

Rather, they’re the result of your body’s natural defenses. When a virus is detected, white blood cells release proteins called cytokines, which recruit more pathogen-fighting immune cells to the area. To aid in this bombardment, blood vessels widen, and it's this inflammation that leads to a blocked, stuffy nose.

The body dials up mucus production in an effort to trap and expel pathogens. But this mucus can irritate and inflame airways, causing coughing and a sore throat. Since the viruses causing colds are so varied, pharmacy products aren't designed to attack viruses, but rather to alleviate the most common symptoms.

So which pill, syrup, or spray should you choose? Or should you ditch the pharmacy and try a home remedy? It depends.

Most pharmacy products contain a painkiller, in addition to one or several other active ingredients, or those mystifying chemical names stamped onto the packaging. While there are over a dozen cold-related ingredients available, most fall into one of four symptom-fighting categories: if you’re sick of dealing with the mucous-y mess oozing from your nostrils, you may want to take nasal decongestants, like pseudoephedrine. This snot-fighter, found in pills and syrups, promotes the release of norepinephrine, a chemical messenger that reduces blood flow to the vessels in your nasal passages.

This frees air and fluid so that you can breathe more easily. Cough suppressants aim to quell those torturous coughs. Dextromethorphan, one of the most common suppressants, addresses the head of the command chain, moderating brain regions responsible for coughing.

While it’s not fully understood how this ingredient manages to quiet coughs, we know it interacts with receptors that neurons use to communicate. Drgs like ketamine and PCP engage similar receptors, which is why it’s important to take dextromethorphan as directed, as high doses are notorious for causing hallucinatory effects. But not all coughing is bad when you have a cold— expelling mucus can help clear out infectious debris and ease uncomfortable congestion.

By lubricating airways, our third class of ingredients, expectorants, aim to help improve coughing rather than eliminate it. Guaifenesin, the most common expectorant, is thought to hydrate mucus by upping fluid secretions in the respiratory tract, making it less sticky and easier to clear out. Finally, we have antihistamines.

As advertised, these inhibit the effects of histamine, the chemical messenger behind allergy symptoms. While histamines aren't involved producing cold symptoms, studies suggest many antihistamines can still help dry a runny nose. Benadryl, for example, contains diphenhydramine, which blocks both the effects of histamine and a neurotransmitter which regulates the flow of mucus in our airways.

Unfortunately histamines also regulate wakefulness in the brain, so many of these drugs can make you drowsy. In this fight against cold symptoms, there’s still a lot we don’t know. Since these ingredients don’t attack the viruses themselves, it’s unclear if any speed up your recovery.

Further, many were first introduced to the market decades ago, when studies were less rigorous. So, scientists continue to reevaluate how well each ingredient relieves symptoms. Similar questions remain around holistic remedies.

Many people use zinc, but research on its effectiveness is inconclusive. And while vitamin C has many benefits, the value of taking large doses to fight a cold is likely overhyped. Yet studies suggest that honey can improve cough and may even shorten your illness by a day or two.

Who knows what the future of cold treatment will look like. Until then, better understanding these products can help you choose the right ones for your symptoms— and know which remedies can best reduce the sting of a nasty cold.