A severe and adverse reaction by the body's immune system to a particular kind of food or a condition is called Allergy. The reaction causing substance is called as Allergens.

All living beings need food for energy. The body's defence mechanism against foreign substances is a strong intestine. It works as a barrier against disease-causing invaders like virus, bacteria and other pathogens.

The defence mechanism and a sound intestine barrier is the key for food tolerance. A damaged or a diseased intestinal barrier may result in chronic inflammation. A hypersensitive reaction which results in a marked increase of an aversion and dislikes to the particular substance for life is called Allergy in medical terms. Food allergy is an intolerance to certain types of food. It can be milk, vegetables, fruits, grains or egg, fish and so on. An allergy to pollen, dust can bring in respiratory problems and allergic reactions.

A person is said to be allergic if he becomes sick after eating, touching or breathing - which can cause adverse reactions in the body. There are environmental factors like pollen which can bring in allergic reactions. And there are dietary factors like sensitivity and intolerance of the person to that particular food, which can cause allergic reactions but surprisingly these may not bring out similar reactions in other people. He becomes susceptible to showing up an allergic reaction every time he comes in contact with or consumes the particular substance again.

The foreign substance triggers an abnormal reaction and causes symptoms in sensitive people whereas others are not affected by these. We have heard many times people complaining about a weak stomach, who cannot tolerate certain types of food, and who are susceptible to allergic reactions. The symptoms can show up as an immediate reaction or as a delayed reaction. Pollen is one good example which can bring about immediate symptoms of running nose, sneezing and headache. Long term allergies can make a person suffer for life with diseases like diabetes and hypertension too.

Some allergic or sensitive reactions that show up immediately are symptoms of nausea, throbbing headache, dizziness, numbness, burning sensation, sneezing, itching, fatigue, extreme weakness, stomach pain, bloating, loose and watery stools, or constipation and so on. Delayed reactions can bring about long-term gastrointestinal problems like Irritable Bowel Disease, Irritable Bowel Syndrome and Crohn's disease, skin rashes, obesity and hypertension. Sometimes the allergens can cause heart palpitations, shortness of breath too, which need immediate treatment in the ICU.

People tend to go in for home remedies for allergic reactions instead of seeking medical help. They can bring in a little relief, and the symptoms can get reduced to an extent, but they can relapse if the cause of the allergy is not identified and treated. Care should be taken to always treat any disease at the cause. With home remedies, the symptoms and pain may reduce over a period but subsequent exposure to the same food or substance can relapse the reactions again. People of old age, very young children, diabetics are all susceptible to allergies very fast.

Types of Allergies can be various. Some of them are listed below. Each of these allergies is as a result of the allergens and show up as different reactions.