How do nasal decongestants work?

Nasal decongestants are medicines that help relieve specific types of congestion – whether you have a blocked nose or sinuses.

Congestion can be caused by lots of different things as it’s a common symptom of a cold, allergies, flu and other conditions. Over-the-counter decongestants can be bought without a prescription to help relieve these symptoms, so you can breathe easier.

Depending on the cause and specific area of congestion, some decongestants may be better than others for easing any pain, blocked passages and additional symptoms.

Learn how decongestants work to help tackle different types of congestion with SUDAFED®.

  • What are nasal decongestants and how do they work?

  • Types of decongestants

  • How long do decongestants take to work?

What are nasal decongestants and how do they work?

Congestion is part of your body’s reaction to a virus, allergen, infection or other illness. The blood vessels in your nose and airways swell, leaving you feeling blocked up.

Most congestion takes place in your nasal passages and sinuses, which can include the Eustachian tube that connects your nose and ear. Decongestants work to reduce the swelling in the blood vessels, helping to open your airways, drain mucus and ease your breathing.

Decongestants don’t treat the underlying cause of congestion, but they can offer temporary relief from symptoms.

There are different kinds of decongestant for different types of congestion. These contain specific ingredients that work to ease congestion and sometimes other related symptoms as well.

Nasal decongestant ingredients

Decongestants all have one primary active ingredient. This varies depending on the type of decongestant and whether it’s a tablet, nasal spray or liquid. They will also have different recommended dosages.

As all decongestants aim to reduce swollen blood vessels to make breathing easier, there are lots of similarities between the primary ingredients.

There are 3 decongestant active ingredients found across the Sudafed range:

  • Pseudoephedrine – One of the most common ingredients in decongestants, pseudoephedrine works to relieve a stuffy or blocked nose and is generally taken in tablet, capsule or liquid form.

  • Phenylephrine – Similar to pseudoephedrine, phenylephrine relieves congestion. It can also be taken as a tablet or liquid.

  • Xylometazoline – This active ingredient can be found in nasal sprays, unlike the other two.

Some decongestants contain additional ingredients that work to tackle other symptoms associated with congestion if you have a cold, flu or other illness. These can include:

  • Caffeine – this can help with the tiredness you may feel when your body is battling an illness where the symptoms include congestion.

  • Guaifenesin – works to loosen mucus, so it’s easier to drain and cough up as congestion eases.

  • Ibuprofen – an anti-inflammatory and painkiller to soothe symptoms of pain.

  • Paracetamol – relieves pain associated with headaches and fevers.

You should avoid taking more than one type of decongestant and always read the label for dosing instructions. If you are unsure, speak to your pharmacist.

Causes of nasal congestion

Knowing the cause of your congestion can help you choose the best decongestant to help relieve your symptoms.


Allergic rhinitis is inflammation of the inside of your nose caused by your immune system reacting to an allergen, such as:

  • Dust

  • Mould

  • Pet dander

  • Pollen

  • Skin flakes.

Hay fever is one of the most common types of allergic rhinitis, which can cause congestion alongside other symptoms, making it difficult to breathe through your nose.

Nasal sprays containing the active ingredient xylometazoline help to relieve congestion to unblock your nose and ease breathing.

Blocked nose

In many cases, a blocked, stuffy nose can be a symptom of a common cold, the flu, allergies or a sinus infection. Decongestants can help to relieve that blocked-up feeling.

Inflamed blood vessels in your nasal sinuses can cause a blocked or stuffy nose. This can stimulate your mucus glands – making them produce more mucus to flush out the cause of the irritation. That’s why you may experience a build-up of mucus alongside a stuffy nose.

The primary aim of a nasal decongestant should be to reduce swelling, so breathing becomes easier and the build-up of mucus subsides. SUDAFED® Blocked Nose Spray is a decongestant for mucus relief, containing xylometazoline that aims to clear blocked airways and reduce stuffiness.


Symptoms of the flu and a common cold can be very similar, and congestion is one of them. With the flu, congestion can come on suddenly, which may mean you need quick relief.

Alongside congestion, you could experience other flu symptoms:

  • An aching body

  • Dry cough

  • Sore throat

  • Headaches

  • Tiredness.

For this reason, many flu nasal decongestants contain additional ingredients to help combat congestion and other related symptoms at the same time.

SUDAFED® Mucus Relief Triple Action Cold & Flu Tablets contain guaifenesin to loosen mucus and paracetamol to help ease pain caused by flu symptoms, in addition to the nasal decongestant phenylephrine.

Head cold

Nasal congestion is one of the main signs of a head or common cold. Pressure in your ears or face may also be a sign of sinus congestion related to a common cold.

Symptoms can be similar to flu but may take longer to develop. While decongestants won’t cure the causes of your cold, they can act to relieve congestion and ease pressure to make you more comfortable.

SUDAFED® Congestion & Headache Relief Max Strength Capsules contains phenylephrine, caffeine and paracetamol to tackle head cold congestion, headache pain and tiredness all-in one.


Our bodies have four pairs of sinuses in the skull and facial bones that allow air and mucus to flow through them. A sinus infection – also known as sinusitis – can occur when the lining of these paranasal sinuses become blocked – sometimes after a cold.

Blocked sinuses stop mucus from draining properly, which can then build up with bacteria, causing a sinus infection and congestion.

Congested sinuses around your nose, forehead and cheekbones can also cause headaches.

SUDAFED® Sinus Pressure & Pain Tablets contain pseudoephedrine to tackle congestion and ibuprofen to offer pain relief and anti-inflammation.

Types of decongestants

Decongestant tablets

To fight congestion caused by colds and flu, the active ingredient pseudoephedrine works to narrow swollen blood vessels. This helps air to flow more easily through your nose, reducing that irritating stuffiness. You can take decongestant tablets orally. Always read the label for correct dosing instructions.

Discover SUDAFED® Decongestant Tablets

Nasal sprays

Relieve unpleasant stuffiness caused by congestion as an allergy, cold or flu symptom with nasal sprays, which starts to provide relief in minutes. The active ingredient xylometazoline works to unblock your nasal passages.

Discover SUDAFED® Blocked Nose Spray

Decongestant liquids

Decongestant liquids are a soothing syrup you take orally that work to reduce nasal swelling, unblocking your nose. They contain the active ingredient pseudoephedrine, which helps to clear nasal congestion. Most are designed for clearing congestion associated with the common cold.

Discover SUDAFED® Decongestant Liquid

How long do decongestants take to work?

How long decongestants take to work can depend on which one you use. Those containing pseudoephedrine, usually found in liquids and tablets, can often start to work from 30 minutes after you’ve taken them.

A decongestant nasal spray that contains xylometazoline works to help provide relief from a blocked nose.

The length of relief provided by a decongestant depends on the product used. Always check the packet for the recommended dosage and guidance on how long it may take to start working.