They are also quite difficult to know what cause them- they are certainly not infectious, but damaging the inside of your cheek accidentally is considered to be one of the main catalysts, along with hormonal change, hereditary, anxiety and certain foods, but they are viscous by nature although they will go as quickly as they came.
They can be treated too- they are some fine gels on sale in most chemists in central Leeds that will get to work quickly on an ulcer. You should also try to avoid abrasive and overly acidic foods until the problem start to subside- painkillers are also an option if the pain is unbearable as are herbal remedies such as clove oil.
Normally, ulcers are more associated with teenage life and although frustrating, they don’t normally hang around for long. If however they are extremely persistent and keep re-offending, you should seek immediate medical help, as it may indicate something more serious and sinister going on in the mouth.