When crystals move into the joint cavity this triggers a gout attack, causing inflammation and pain in the soft lining of the joint.
A swollen, red painful big toe is one of the classic symptoms of gout, although crystals can grow in any joint. During a gout attack or flare up, joints can become red and inflamed and extremely painful and shiny red skin can appear over the joint. Attacks normally die down after three to 10 days as the inflammation settles down.
Tophi, small white hard lumps of crystals visible under the skin can also form in the soft tissue (including the ear), and these can eventually form in joints and damage them.
Gout is caused by chemical called urate building up, and crystals forming in and around joints.
Although a diet rich in red meat and too much alcohol is often blamed for gout and can be triggers for attacks, the most common cause is genetic. Some people are genetically predisposed to not clearing urate from their bodies quickly enough.
Other factors such as your weight (if you're heavier your body produces more urate) can also make you more prone to gout. If you have type 2 diabetes, high cholesterol and high blood pressure these can all affect your kidney function and make it harder to flush out urate and raise your risk.
Blood tests can measure how much urate is concentrated in your blood but can't be used to diagnose gout on its own, as its possible to have raised levels of urate and not have crystals in your joints and for urate levels to be normal during an attack.
X-rays can confirm joint damage from long-standing gout and fluid can be extracted from the space between joints to test for the presence of urate crystals.
Who gets gout?
Gout affects 2.5 per cent of the UK population and it's more common in men than women. It mainly affects men over 30 and post-menopausal women. It's become a lot more common in recent years and this is thought to be due to rising levels of obesity.
You may be more at risk of gout if your parents or grandparents have had it as this means you may have inherited a genetic predisposition to not be able to clear urate from your body quickly enough.
As mentioned above, you may be more at risk if you have high blood pressure, raised cholesterol and type 2 diabetes and are overweight.
If you have a gout attack, treatments include anti-inflammatory drugs and a drug called colchicine or steroids, as well as resting and elevating the affected area, applying ice and trying to avoid knocking it.
The drugs allopurinol and febuxostat both reduce levels of uric acid to help prevent attacks coming back and sulfinpyrazone and benzbromarone can be prescribed if people are unable to take either allopurinol or febuxostat.
Changing your lifestyle by losing weight, drinking more fluids and cutting down on alcohol including beer and spirits can help prevent attacks. Research has also shown that reducing your intake of foods containing purines, chemicals involved in the production of uric acid, can also help, one study found eating purine-rich foods increased the risk of recurrent attacks in people with gout by five times. Purine-rich foods include red meat, offal and seafood.
Some research suggests cherries and cherry extract can help. In one study, cherry and cherry extract intake was associated with a 35 per cent reduction in recurrent gout attacks in those with the condition. When cherry intake was combined with taking allopurinol, it reduced attacks by 75 per cent.