Childhood food allergies are apparently much more common in America than previously believed. A clinical study, recently published in the journal Pediatrics, found that about 8 percent of children under the age of 18, almost 6 million, suffer from one or more food allergies.

The numbers are twice as high as the latest data released by the Centers for Disease Control and Prevention (CDC) in 2007, which showed a rate of just under four percent, or about three million kids.

The new findings came from online interviews that included 40,000 households all over the United States. Participants were recruited through random telephone calls. Based on the information gathered from the survey, experts now believe that allergies among the young, including food allergies, are dramatically on the rise.

“Based on our data, about one in 13 children has a food allergy,“ Dr. Ruchi Gupta said, assistant professor of pediatrics at Northwestern University Feinberg School of Medicine in Chicago and lead author of the report. “What’s more, nearly two out of every five affected children suffer from a severe food allergy. For these children, accidental ingestion of an allergenic food may lead to difficulty breathing, a sharp drop in blood pressure, and even death.”

Dr. Gupta, who also works as a pediatrician at Chicago’s Children’s Memorial Hospital, acknowledges that her study provides only a snapshot of the prevalence of food allergies in America today and does not track developments over time. Still, she says, “eight percent is a pretty significant amount. […] We are seeing a lot more cases in schools than we used to see. It does seem that food allergy is on the rise.”

The CDC estimates that eight types of foods are responsible for 90 percent of all food allergies in children. They are milk, eggs, peanuts, tree nuts, fish, shellfish, soy and wheat.

Allergy is a condition that occurs when a person’s immune system is hypersensitive or over-reactive. Ordinarily, the human immune system has the ability to distinguish between harmless substances in the environment and potentially harmful agents, such as viruses and bacteria. For a person with allergies, however, the immune system reacts swiftly and with great intensity to substances that are not dangerous as if they were. So, when an individual who has certain allergies eats, touches or inhales an allergen (a foreign substance he or she is allergic to), the immune system mistakenly responds with an all-out counterattack.

Many experts believe that the tendency to develop allergies is primarily hereditary. However, in addition to genetic traits, long-term exposure to certain health hazards in the environment, such as tobacco smoke, pesticides and other pollutants, can provoke allergic reactions. So can emotional factors and other stressors.

People who suffer from food intolerances are not necessarily allergic to these foods. The symptoms can be similar, but with intolerance the physical reactions are usually due to problems with digestion. For instance, people with lactose intolerance are unable to produce enough of a digestive enzyme needed to break down milk sugar. They are lactose intolerant, but the immune system is not involved in the resulting digestive distress.

There can be conditions, however, where food intolerances and allergies sort of overlap. Celiac disease, for example, generates an abnormal immune response to foods containing gluten, like wheat and some grain products. Despite of this, celiac disease is classified as a food intolerance, although it is triggered by autoimmune activity.

Another difference between food intolerances and allergies is that the symptoms of intolerances generally intensify with age, while those of allergies get worse with exposure.

Allergies should not be taken lightly, especially when children are affected. Possible reactions range from mild to severe. They include swelling of lips and face, hives, itching, flushing or eczema flare. The severest cases, known as anaphylaxis, are potentially life-threatening. Symptoms include wheezing, trouble breathing, vomiting, persistent coughing and dangerous swelling of the airways.

“Especially for kids with multiple food allergies, it complicates their lives and makes it really tough on these kids to avoid multiple foods to stay healthy and stay alive,” says Dr. Gupta.

Parents of children with serious food allergies are urged to always carry antihistamine as well as an epinephrine shot (EpiPen) with them. The most effective measure people can take against allergic reactions is avoidance. That means paying close attention to ingredient labels, taking precautions when eating at restaurants and bringing along one’s own food if safe alternatives are unavailable.

Many children outgrow their allergies or tolerate them better as they grow older, including those against milk, eggs and wheat, while peanuts, tree nuts and shellfish often remain a lifetime threat.

Timi Gustafson R.D. is a clinical dietitian and author of the book “The Healthy Diner – How to Eat Right and Still Have Fun.”