Adverse reactions to something you've eaten can range from mild digestive discomfort to rashes or even, in rare cases, to an extreme life-threatening allergic response. Fortunately, the latter is relatively uncommon although the numbers of people affected do seem to be rising.
Related: Is it something you ate? Food intolerance, causes and diagnosis
Experts distinguish between intolerance and a true allergic reaction although, in many cases, the difference would not be apparent to the person involved.
The distinction relates to the precise nature of the body's response to the culprit food: if you are genuinely allergic, there will be a measurable immune system reaction in that various substances are released to 'attack and destroy' the food which it mistakenly regards as it would a bacterial or viral invasion.
The result may be a skin rash, hay-fever-type symptoms, swelling in the mouth and around the lips and digestive upset. Should you ever experience these symptoms, you would be well advised to consult your doctor as it is possible that they might be more severe on any subsequent occasion.
If appropriate, your doctor may arrange tests at a hospital clinic to establish whether you are experiencing a potentially serious allergy and, if so, to attempt to identify the foods responsible.
Among the more common food allergens are cows' milk and foods made from it, eggs, wheat and other cereals, fruit such as strawberries, nuts and shellfish.
If tests or experience indicate that any of these foods cause problems for you, the only solution is to do everything you can to avoid consuming them in future. In some cases, this may mean questioning restaurant staff about the ingredients of a dish before ordering it and you may also need to study the ingredients list on food packaging when shopping.
Related: Coeliac disease and other wheat-related disorders
Although you may be certain in your own mind that certain foods cause problems for you, the precise culprits can be much more difficult to identify if you are suffering from food intolerance or sensitivity rather than a true allergy.
Partly this is because there are unlikely to be any physiological changes which can be measured by reliable tests, and partly because the symptoms are often less clear-cut and may only appear some time after you have consumed the offending food.
You may feel sick or bloated or just that your digestive system is upset and it often takes a lot of detective work to identify the cause. One useful step is to keep a detailed food diary for at least two weeks, recording everything you eat and drink and the timing and nature of any symptoms. In time, it may be possible recognise a pattern that links what you've eaten to your symptoms.
If this doesn't help, the other approach is an elimination diet, in which you eat only a small range of foods for a set period and gradually reintroduce more to see whether you get a reaction. However, this approach should only be tried with the help of your doctor or a dietician as it can lead to you becoming under-nourished and there is also a risk of triggering severe symptoms when a 'culprit' food is re-introduced.
Related: Gut instinct - recognising bowel disorders
From time to time you may see advertisements for tests which claim to identify food allergies and intolerance using hair samples, electronic devices which measure energy flow or acupressure points, among other things.
All these have to be paid for privately and, not only is there no scientific evidence that they work, they may also come up with false positive results.