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If you've suffered from a blocked nose and sinus pain, the chances are that you'll have reached for a decongestant.

But you may not know how the remedy relieves the annoying symptoms.

Now, a chemistry teacher from Bournemouth has created an infographic to explain just how the medicine, which typically comes in spray or tablet form, stops the nose from running.

Chemistry Andy Brunning created an infographic (pictured) to explain how decongestants work. They targetalpha-adrenergic receptors in the nose and sinuses to constrict blood vessels, which helps to reduce inflammation and the formation of mucus

Andy Brunning explained in a post on his blog, Compound Interest that decongestants work by targeting alpha-adrenergic receptors in the nose and sinuses to constrict blood vessels, which helps to reduce inflammation and the formation of mucus. 

While a number of drugs can be used to create the effect, some of the most common are pseudoephedrine, oxymetazoline - which can also be used to treat nosebleeds - phenylephrine and xylometazoline.

Pseudoephedrine, a natural compound found in plants, is one of the most effective decongestants and is produced on a large scale by using a mixture of yeast, dextrose – grape sugar - and benzaldehyde, which is a colourless liquid with many industrial uses.

As well as acting on alpha-adrenergic receptors, pseudoephedrine also targets other receptors, which relax muscles in the airways to ease congestion.

As well as acting on alpha-adrenergic receptors, pseudoephedrine also targets other receptors, which relax smooth muscle in the airways to ease congestion (illustrated in this stock image) But using the decongestant for too long can backfire

While pseudoephedrine is an ingredient in may over-the-counter medicines, there are other active ingredients.

Phenylephrine is one such alternative, but a handful of studies have claimed it is no more effective in easing nasal congestion than a placebo.

Xylometazoline, on the other hand, is on the World Health Organisation's list of essential medicines, but isn't advised for people with high blood pressure.

Oxymetazoline can also be used in the treatment of nosebleeds and eye redness.

While nasal decongestants may be effective in relieving the symptoms of a cold in the short term, they can only be used for a limited amount of time.

'For the most part, use of nasal sprays for more than a few days can induce rhinitis medicamentosa, more commonly referred to as rebound congestion,' Mr Brunning writes.

Scientists are unsure exactly why this happens, but it means that people who overuse their nasal sprays can trigger a vicious circle of mucus.

'More of the decongestant is taken to alleviate the congestion, and the rebound congestion continues,' he explained.

It seems that the problem of rebound congestion can be avoided by taking tablets instead.