Blepharitis is a common inflammation of the eyelids. It is often a persistent condition with no 'one-off' cure.
There is no one reason, it just happens. It is not due to anything you have done or not done, although rubbing your eyelids will make the inflammation worse.
Blepharitis can cause your eyes to produce fewer tears. This will give a gritty and sore feeling. If eyelid cleaning does not resolve these symptoms you may need to use artificial tear drops. These can be purchased from your local Duncan and Todd branch, pharmacist or prescribed by your GP. They will be happy to discuss the artificial tear best suited for you.
Do not use artificial tears when wearing your contact lenses, and consult your specialist if you are already using eyedrops for other conditions (such as glaucoma).