Nasal decongestants work by narrowing the blood vessels inside your nose, which shrinks swollen tissue and opens your airway. That stuffy feeling isn’t caused by mucus alone. It’s mostly caused by engorged blood vessels in your nasal lining, and decongestants target those vessels directly.
Why Your Nose Gets Stuffed Up
The inside of your nose is lined with soft tissue called the nasal mucosa, and embedded in that tissue are networks of tiny blood vessels, particularly in structures called the inferior turbinates. These are ridges along the walls of your nasal passages that warm and humidify the air you breathe. The turbinates contain a dense web of expandable blood vessels (venous sinusoids) that can fill with blood and swell on demand, controlled by your autonomic nervous system.
When you get a cold, allergies, or a sinus infection, inflammation triggers these blood vessels to dilate and fill with extra blood. The turbinate tissue swells, sometimes dramatically. Because the nasal passages are narrow to begin with, even a small increase in tissue thickness significantly increases resistance to airflow. That’s congestion: not a blockage of dried mucus, but puffy, blood-engorged tissue physically narrowing your airway.
How Decongestants Shrink the Swelling
Decongestants are sympathomimetic drugs, meaning they mimic the effects of your sympathetic nervous system, the same system that kicks in during a “fight or flight” response. They activate receptors on blood vessel walls called alpha-adrenergic receptors, which signal the smooth muscle around those vessels to contract. The vessels narrow, blood flow to the nasal tissue drops, and the swollen sinusoids shrink. With less blood pooling in the tissue, the mucosa thins out, the airway opens, and you can breathe again.
Some decongestants do this directly by binding to those receptors themselves. Others work indirectly by triggering the release of norepinephrine, your body’s own vasoconstricting chemical, from nearby nerve endings. Either way, the end result is the same: constricted blood vessels, reduced swelling, and freer airflow.
Sprays vs. Pills
Decongestants come in two main forms, and the differences matter more than you might expect.
Nasal sprays (containing ingredients like oxymetazoline or phenylephrine) deliver the drug directly to the nasal lining. They work fast, often within minutes, because the active ingredient hits the swollen tissue immediately. The tradeoff is a shorter window of appropriate use. After about three days of regular use, the spray can actually make congestion worse through a process called rebound congestion. The sustained constriction deprives nasal tissue of the nutrient-rich blood it needs, which leads to tissue irritation and, paradoxically, more inflammation and swelling than you started with. This cycle can be difficult to break.
Oral decongestants (like pseudoephedrine) are swallowed, absorbed into the bloodstream, and carried to the nasal vessels from the inside. They take longer to kick in but generally last longer per dose. Because they circulate throughout the body rather than concentrating in one spot, they don’t cause rebound congestion. They do, however, affect blood vessels everywhere, which is why they can raise blood pressure and increase heart rate.
The Oral Phenylephrine Problem
For years, one of the most common oral decongestants on store shelves has been phenylephrine. It’s the active ingredient in many popular cold medicines. But in 2023, an FDA advisory committee unanimously concluded that oral phenylephrine, at the recommended over-the-counter dose, does not actually work as a nasal decongestant. The FDA has since proposed removing it from the approved list of OTC decongestant ingredients.
The issue is specific to the oral form. When you swallow phenylephrine, your gut and liver break down most of it before it ever reaches your bloodstream in meaningful amounts. Phenylephrine in a nasal spray still works because it’s applied directly where it’s needed. But the pills sitting on pharmacy shelves are, based on current evidence, no more effective than a placebo for relieving congestion. As of now, companies can still sell these products while the FDA finalizes its ruling. If you’re buying an oral decongestant, pseudoephedrine (typically kept behind the pharmacy counter) remains the one with solid evidence behind it.
Blood Pressure and Heart Effects
Because decongestants constrict blood vessels, they don’t limit their effects to your nose when taken orally. The same mechanism that shrinks nasal tissue can tighten blood vessels throughout your body, producing a temporary rise in blood pressure. For most healthy adults, this bump is minor. But if you already have high blood pressure, particularly if it’s not well controlled, oral decongestants can push readings into concerning territory and interfere with the effectiveness of blood pressure medications.
Extended-release formulations tend to produce a smaller spike than immediate-release versions, though they can still cause problems for people with cardiovascular concerns. Nasal sprays, because they act locally, have much less systemic effect on blood pressure, which is one reason they’re sometimes preferred for people with heart conditions, provided you stick to the three-day limit.
Age Restrictions for Children
Decongestants carry real risks for young children. The FDA warns that children under two should never be given any cough and cold product containing a decongestant, citing reports of serious side effects including seizures, dangerously rapid heart rates, and deaths. Manufacturers have voluntarily relabeled these products to say “do not use in children under 4 years of age.”
For children four and older, over-the-counter decongestants can be used with caution. The key risks come from giving more than the recommended dose, giving doses too frequently, or accidentally doubling up by using two products that contain the same active ingredient. Adult formulations should never be given to children.