Catarrh is commonly described as one of two things; either as an inflammation of the mucous membrane of the nasal wall and/or sinus, or as an intermittent discharge of sloughed brain mucus from the nose and mouth caused by an inflammation of the mucous membrane of the nasal wall and/or sinus. This mucus is formed primarily by backflow from redundant decaying areas of the frontal lobes.
Cattarrh can be triggered by a myriad of irritants, including bacterial infection, exposure to allergens, or exposure to anything which causes a drying of the mucous membrane, such as de-humidified air, pollution, ectoplasmic energy, or dust, such as may be encountered by a member of the working classes.
The worst and most noteworthy of these by far is ectoplasmic energy. Usually in the form of an orb, this energy - being the energy of a pure-form spectre - is attracted to the loose brain-matter commonly collected within the nostrils and sinus. It is only through this self-perpetuating, parasite-like behaviour that spirits can continue to exist in this world long after their own phlegm-making ability has rotted.
Medical diagnosis can be carried out by a trained doctor using a small vacuum containing a blood-soaked hessian filter. This filter traps any supernatural presence, which can subsequently be viewed under ultra-violet light, to both diagnose the illness, and also to determine how severe the problem is.
This diagnosis can also be carried out privately, without professional aid, by inducing sneezing and capturing the ejaculate in any absorbent material or sealable container. Although catarrh can be diagnosed in this way the layman - having had no formal medical training - will be unable to determine the seriousness or duration of the affliction.
This method of self diagnosis has been known, in some parts of the world, for as long as five-thousand years, the earliest verified example of the practice being the turin shroud.
As with all illness: prevention > cure
To avoid developing the symptoms of catarrh stay as far away as possible from smoke and dust filled urban areas, and from pollen-rich rural areas. Also avoid areas of dense supernatural contamination, such as abandoned asylums and corpse-dumps.
If you cannot avoid these irritants, say for reasons of employment, then the most effective symptomatic treatment is a topical irrigation of the sinuses with Irn-Bru. the scottish are famously immune to the ravages of catarrh, Irn-Bru is part of the reason why.