• abdominal pain and cramping, which is often relieved by emptying your bowels
• a change in your bowel habits, such as diarrhoea, constipation or sometimes both
• bloating and swelling of your abdomen
• excessive wind (flatulence)
• an urgent need to go to the toilet
• a feeling that your need to open your bowels even if you've just been to the toilet
• a feeling that you have not fully emptied your bowel
• passing mucus from your back passage

Not surprisingly, given the embarrassment, pain and discomfort of IBS, many people with the condition also have symptoms of depression and anxiety.

Bowel symptoms

There are three main patterns of bowel symptoms in IBS. They are:

• IBS with diarrhoea: when you have repeated bouts of diarrhoea
• IBS with constipation: when you have repeated bouts of constipation
• IBS mixed: when you have repeated bouts of diarrhoea and constipation

These patterns aren't set in stone. You can switch from one to another and go for long periods with few or no symptoms at all.

This can be due to:

• a change in your body's ability to move food through your digestive system
• you becoming more sensitive to pain from your gut 
• psychological factors

Food movement through the gut

Normally, your body moves food through your digestive system by squeezing then relaxing the muscles of the intestines in a rhythmic way.

If you have IBS, it's thought this process is disrupted, so food moves through your digestive system too quickly or too slowly. Moving too quickly results in diarrhoea because your digestive system does not have enough time to absorb water from the food. If food moves too slowly, the result is constipation, because too much water is absorbed, which makes stools hard and difficult to pass.

Theories suggest that, in people with IBS, food doesn't pass through the digestive system properly because the signals that travel back and forth from the brain to the gut, controlling the muscles, are disrupted in some way.

An increase in levels of the chemical 5-hydroxytryptamine (5-HT) which can happen after eating certain foods or during times of stress is also thought to affect the normal process of the digestive system.

Increased sensitivity

Many sensations in the body come from your digestive system. For example, nerves in your digestive system relay signals to your brain to let you know if you are hungry or full, or if you need to go to the toilet.

Some experts believe that if you have IBS you are oversensitive to these digestive nerve signals so mild indigestion that is barely noticeable in most people becomes distressing abdominal pain.

Psychological factors

There's a lot of evidence that psychological factors play an important role in IBS.

This doesn't mean that IBS is "all in the mind" – the symptoms are very real. But intense emotional states, such as stress and anxiety, can trigger chemical changes that interfere with the normal workings of the digestive system.

This doesn't just happen in people with IBS. Many people who have never had IBS can have a sudden change in bowel habits when faced with a stressful situation, such as an important exam or a job interview.

It's also been found that many people with IBS have experienced a traumatic event, usually during their childhood, such as abuse, neglect, a serious childhood illness or bereavement.

It is possible that difficult experiences in your past, such as these, make you more sensitive to stress and the symptoms of pain and discomfort.

IBS triggers

Certain foods and drinks can trigger IBS symptoms. Triggers vary from person to person but the most common ones include:

• alcohol
• fizzy drinks
• chocolate
• drinks that contain caffeine, such as tea, coffee or cola
• processed snacks, such as crisps and biscuits
• fatty food
• fried food

Keeping a food diary may be a useful way of identifying possible triggers in your diet.

Another common trigger of IBS symptoms is stress. So, finding ways to cope better with stressful situations is an important part of treating IBS.

Read more about treating IBS.

However, if you have the symptoms of IBS, your GP will usually recommend that you have a blood test to rule out other conditions that cause similar symptoms, such as an infection or coeliac disease (a stomach condition caused by gluten intolerance).

Your doctor will generally diagnose IBS by seeing if your symptoms match those that are typical of the condition.

Your doctor will suspect that you have IBS if one of the following applies to you:

• You have abdominal pain or bloating that is relieved when you pass a stool.
• You have abdominal pain or bloating associated with episodes of diarrhoea or constipation.
• You are passing stools more frequently than normal.

Having at least two of the following symptoms should confirm that you have IBS:

• a change in how you pass stools, such as needing to strain, feeling a sense of urgency or feeling that you haven't emptied your bowels properly
• bloating, hardness or tension in your abdomen
• your symptoms get worse after eating
• you pass mucus from your back passage

Further tests

Further tests are usually only needed when you have certain "red flag" symptoms that indicate that you may have a more serious condition than IBS. These symptoms include:

• unexplained weight loss
• a swelling or lump in your abdomen or back passage
• bleeding from your back passage
• anaemia

Further testing may also be recommended if you have a family history of bowel or ovarian cancer, or if you are over 60 years old and you've had a change in your bowel habits that has lasted for more than six weeks.

The types of test that you may have are:

• a sigmoidoscopy – where a device called a  a thin, flexible tube that is attached to a small camera and light (sigmoidoscope) is used to examine your back passage and the lower section of your bowel
• a colonoscopy – where a device similar to a sigmoidoscope, called a colonoscope, is used to examine your entire bowel  

IBS-friendly diet

Changing your diet is a key way to control the symptoms of IBS. However, there is no "one size fits all" diet for people with IBS. The diet that will work best for you depends on your symptoms and how you react to different foods.

You may find it helpful to keep a food diary and record whether certain foods make your condition better or worse. Once you identify any particular foods that trigger it, you can avoid them.

Fibre

People with IBS are often advised to modify the amount of fibre in their diet. There are two main types of fibre:

• soluble fibre, which the body can digest
• insoluble fibre, which the body cannot digest

Food containing soluble fibre include:

• oats
• barley
• rye
• fruits such as bananas and apples
• root vegetables such as carrots and potatoes
• golden linseeds

Foods containing insoluble fibre include:

• wholegrain bread
• bran
• cereals
• nuts and seeds (except golden linseeds)

If you have IBS with diarrhoea, you may find it helps to cut down on the insoluble fibre you eat. It might also help to avoid the skin, pith and pips from fruit and vegetables, too.

If you have IBS with constipation, it can help if you increase the amount of soluble fibre in your diet and increase the amount of water you drink.

Your GP can advise you on what your recommended fibre intake should be.

NICE (the National Institute for Health and Clinical Excellence) has more detailed advice about foods to eat or avoid when you have IBS.

Eating tips

Your IBS symptoms may improve with these tips:

• Have regular meals and take your time when eating.
• Avoid missing meals or leaving long gaps between eating.
• Drink at least eight cups of fluid a day, particularly water and other non-caffeinated drinks, such as herbal teas.
• Restrict your tea and coffee intake to a maximum of three cups a day.
• Reduce your intake of alcohol and fizzy drinks.
• Reduce your intake of "resistant starch" (starch that resists digestion in the small intestine and reaches the large intestine intact). It is often found in processed or re-cooked foods.
• Limit fresh fruit to three portions a day. A suitable portion would be half a grapefruit or an apple.
• If you have diarrhoea, avoid sorbitol, an artificial sweetener that is found in sugar-free sweets, including chewing gum and drinks, and in some diabetic and slimming products.
• If you have wind and bloating, consider increasing your intake of oats. For example, oat-based breakfast cereal or porridge and linseeds (up to one tablespoon a day).

Never start a food-avoidance and exclusion diet (where you avoid eating a class of food, such as dairy products or red meat) unless you're doing so under the supervision of a professional dietitian.

Exercise

Most people find exercise helps to relieve IBS symptoms.

Your GP can advise you about the type of exercise that is suitable for you.

Aim to do a minimum of 30 minutes of vigorous exercise a day, at least five times a week. The exercise should be strenuous enough to increase your heart and breathing rates. Walking briskly and walking up a hill are both examples of vigorous exercise.

Some people find that taking probiotics regularly can help to relieve the symptoms of IBS. Probiotics are dietary supplements that contain "friendly bacteria" and are available at most supermarkets.

You may need to take probiotics for several weeks before you notice any beneficial effect. Make sure you follow the manufacturer’s instructions and recommendations.

Reducing stress

Reducing the amount of stress in your life may help to reduce the frequency and severity of your IBS symptoms. Some ways to help relieve stress include:

• relaxation techniques, such as meditation or breathing exercises
• physical activities, such as yoga or Tai Chi 
• regular exercise, such as walking, running or swimming

If you're particularly stressed, you may benefit from a talking therapy, such as stress counselling or cognitive behavioural therapy (CBT).

Medication

A number of different medications are used to help treat IBS. These are:

• antispasmodic medicines, which help to reduce abdominal pain and cramping
• laxatives, which help to treat the symptoms of constipation
• antimotility medicines, which help to treat the symptoms of diarrhoea
• antidepressants, which were originally designed to treat depression but can also reduce abdominal pain and cramping

Antispasmodic medicines

Antispasmodic medicines work by helping to relax the muscles in your digestive system. Examples of antispasmodic medicines include Colofac (mebeverine) and therapeutic peppermint oil.

Side effects with antispasmodic medicines are rare. However, people taking peppermint oil may have occasional heartburn and irritation on the skin around their anus.

Antispasmodic medicines are not recommended for pregnant women.

Laxatives

Bulk-forming laxatives are the type of laxative usually recommended for people with IBS-related constipation. They work by making your stools denser and softer, which makes them easier to pass.

It's important that you drink plenty of fluids while using a bulk-forming laxative. This helps to prevent the laxative causing an obstruction in your digestive system.

Start on a low dose and then, if necessary, increase it every few days until one or two soft stools are produced every one or two days. Don't take a bulk-forming laxative just before going to bed.

Side effects of taking laxatives can include bloating and wind. However, if you increase your dose gradually you should have few, if any side effects.

Antimotility medicines

The antimotility medicine loperamide is usually recommended for IBS-related diarrhoea.

Loperamide works by slowing the contractions of the muscles in the bowel, which slows down the speed at which food passes through your digestive system. This allows more time for your stools to harden and solidify.

Side effects of loperamide include:

• abdominal cramps and bloating
• dizziness
• drowsiness
• skin rashes

Loperamide is not recommended for pregnant women.

Antidepressants

There are two types of antidepressants that are used to treat IBS – tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs).

Tricyclic antidepressants (TCAs) are usually recommended when antispasmodic medicines haven't been enough to control the symptoms of pain and cramping. They work by relaxing the muscles in your digestive system.

Side effects include dry mouth, constipation, blurring of vision and drowsiness, but should ease after 7 to 10 days as your body gets used to the medication.

Tell your GP if the side effects become a problem, as they can prescribe a type of antidepressant.

The most widely used TCA is called amitriptyline.

Selective serotonin reuptake inhibitors (SSRIs) are an alternative antidepressant.

Examples of SSRIs used to treat IBS include:

• citalopram
• fluoxetine
• paroxetine

Common side effects of SSRIs include blurred vision, diarrhoea or constipation and dizziness.

Read more about selective serotonin reuptake inhibitors (SSRIs).

Psychological treatments

If your IBS symptoms are still troublesome after 12 months of treatment, your GP may refer you for a type of therapy known as a psychological intervention.

There are several different types (detailed below), which all work by teaching you techniques to help you control your condition better. The availability of psychological interventions on the NHS may vary from region to region.

Hypnotherapy

Hypnotherapy has been shown to help some people with IBS to reduce their symptoms of pain and discomfort.

Hypnosis is used to change your unconscious mind’s attitude towards your symptoms.

You can have hypnotherapy as an outpatient in some NHS hospital pain clinics, or you can learn self-hypnosis techniques to do at home.

Psychodynamic interpersonal therapy (PIT)

Psychodynamic interpersonal therapy (PIT) is a type of talking treatment that has had some success in helping people with IBS.

It's a form of psychotherapy based on the principle that your unconscious thoughts, beliefs and attitudes can influence how you think, act and feel.

Your therapist will help you to explore how your past might have unconsciously affected you. They will also help you to confront unhelpful beliefs, attitudes and behaviours, to try to change them.

Cognitive behavioural therapy (CBT)

Cognitive behavioural therapy (CBT) is another talking treatment that can help with IBS.

CBT is based on the principle that the way that you feel depends partly on the way that you think.

Studies have shown that if you train yourself to react differently to your IBS by using relaxation techniques and staying positive, you should see a decrease in your pain levels.

CBT may also help you to cope better with stress, anxiety and depression.

Complementary therapies

There are several complementary therapies that are sometimes claimed to help IBS, including:

• acupuncture
• reflexology
• aloe vera
• colonic irrigation

However, there's no evidence to suggest that these therapies are effective in treating IBS. Also, be aware that aloe vera has been linked to a number of side effects, such as dehydration and a reduction in blood sugar levels.

But the pain, discomfort and inconvenience of IBS is very real and can often have a deep psychological effect.

It's estimated that three out of four people with IBS will have at least one bout of depression and just over half will develop generalised anxiety disorder (GAD) – a long-term condition that can cause overwhelming emotions of anxiety, fear and dread.

If you have feelings of depression or anxiety and they're affecting your daily life, contact your GP because these conditions rarely improve without treatment.

Also, being anxious and depressed could make your IBS symptoms worse.

There are a range of effective treatments for depression and GAD. They include antidepressant medicines and cognitive behavioural therapy (CBT), or a combination of the two.