The substance in a food that can cause an allergic reaction in certain people is called an allergen. There is generally more than one kind of allergen in each food. Most allergic reactions to food are mild but a small proportion of people with a food allergy can have severe reactions. The symptoms of food allergy can affect almost any part of the body, including the skin, the heart, and the respiratory and gastrointestinal systems. Symptoms can appear within minutes, or up to several hours after the person has eaten the food they are allergic to. They can include: -- rashes (usually very itchy) -- tingling sensation in the mouth -- swelling of the lips, tongue, face and throat -- difficulty breathing -- diarrhoea -- vomiting -- abdominal cramps On rare occasions, food allergy can also cause a rapid drop in blood pressure and loss of consciousness. These symptoms are usually linked to a life-threatening form of allergy known as anaphylaxis (pronounced anna-fill-axis). Anaphylaxis, sometimes called anaphylactic shock, can be fatal if not treated immediately, usually with an injection of epinephrine (adrenaline). When someone has an anaphylactic reaction, they can have symptoms in different parts of the body at the same time, causing rashes, swelling of the lips and throat, difficulty breathing and a rapid fall in blood pressure. The first symptoms of anaphylaxis can develop within minutes and severe breathing difficulties can develop up to several hours after eating the food. Many anaphylactic reactions can be misleadingly mild at first, so it's better to be cautious and not underestimate the danger. People with asthma are more likely to have a severe reaction affecting the lungs. Anaphylaxis can also be caused by other things, such as bee and wasp stings, and drug allergy, but food allergy is one of the most common causes. Peanuts, milk, eggs and fish are the most common foods to cause anaphylaxis in the UK and Europe. Nuts, sesame seeds and shellfish can also cause it. Generally, the symptoms of food allergy are more severe than other types of food intolerance. When someone has a food allergy, a tiny amount of the problem food can cause a reaction, but usually the symptoms of other types of food intolerance are caused by larger amounts. Often the symptoms of food intolerance start some time after eating the food, which can make the condition difficult to diagnose. ORAL ALLERGY SYNDROME Certain foods, particularly fruit and vegetables, can cause reactions such as itching or rashes when they touch the lips and mouth. This is called oral allergy syndrome and is a symptom of food allergy. These reactions usually happen in people who are sensitive to pollen, for example pollens from birch, grass, or plants in the daisy family such as ragweed and mugwort. This is because the protein in these pollens, which certain people react to, is also found in some fruit and vegetables. For example, a person who is sensitive to ragweed pollen may develop rashes on the lips when they eat melon, and someone who is sensitive to birch tree pollen may react to apples. Cooking often destroys the allergens that cause this kind of reaction in fresh fruit and vegetables so, for example, people who react to raw apples might be able to eat cooked apples. EXERCISE-INDUCED FOOD ALLERGY This is when someone has an allergic reaction to a particular food when they eat it just before they exercise. People who are sensitive in this way may normally be able to eat the food with only a mild reaction, or no reaction at all, but they can have a severe reaction (including anaphylaxis) if they eat it just before they exercise. ALLERGIC CROSS-REACTION Sometimes, if someone has an allergy to one thing they will also react to other things. This can happen because different foods (or substances) contain either the same allergen or an allergen with a similar structure. This means different foods can cause similar allergic reactions, which is known as allergic cross-reaction. Allergic cross-reaction means that someone could suffer an allergic reaction even when they're avoiding the foods they know they're allergic to. For example, if someone is allergic to peanuts, they might also react to other legumes such as soya, peas, lentils and beans. Allergic cross-reactions can also happen between certain fruit or vegetables and latex (known as latex-food syndrome), or the pollens that cause hayfever. Only some people who have food allergies will experience allergic cross-reaction. Some food allergies can also be linked because of what is known as an 'associated reactivity'. This means that although the substances don't contain the same allergen, it's quite common for people who are allergic to one substance also to react to another substance. For example, people with peanut allergy are often allergic to nuts or eggs too. And people who are allergic to soya might also be sensitive to milk.

Researchers in Spain have discovered that a cannabis extract makes brain tumors shrink by halting the growth of blood vessels that supply the tumors with life. Cannabis has chemicals called cannabinoids, these are the chemicals that could effectively starve tumors to death, say the researchers.

The study was carried out at the Complutense University, Madrid, Spain.

The team used mice to demonstrate that the cannabinoids block vessel growth.

You can read about this latest research in the journal Cancer Research.

Apparently, the procedure is also effective in humans.

The Spanish team, led by Dr Manuel Guzm�n, wanted to see whether they could prevent glioblastoma multiforme cancer from growing by cutting off its blood supply. Glioblastoma multiforme is one of the most difficult cancers to treat - it seldom responds to any medical intervention, such as radiotherapy, chemotherapy and surgery.

The scientists knew that cannabinoids will block the growth of blood vessels (to tumors) in mice - they wanted to find out whether the same thing would happen with humans.

The mice were given a cancer similar to the human brain cancer (glioblastoma multiforme). The mice were then given cannabinoids and the genes examined.

The genes associated with blood vessel growth in tumors through the production of a chemical called vascular endothelial growth factor (VEGF) had their activity reduced.

Cannabinoids halt VEGF production by producing Ceramide. Ceramide controls cell death.

Dr Guzm�n said: "As far as we know, this is the first report showing that ceramide depresses VEGF pathway by interfering with VEGF production."

They then wanted to see if this would also happen with humans.

They selected two patients who had glioblastoma multiforme and had not responded to chemotherapy, radiotherapy or surgery. The scientists took samples from them before and after treating them with a cannabinoids solution - this was administered directly into the tumor.

Amazingly, both patients experienced reduced VEGF levels in the tumor as a result of treatment with cannabinoids.

The researchers said that the results were encouraging. In order to be sure about their findings they need to carry out a larger study, they said.

Dr Guzm�n said "The present findings provide a novel pharmacological target for cannabinoid-based therapies."